clarify backwards-compatibility policy (CASSANDRA-3951)
clarify backwards-compatibility policy (CASSANDRA-3951)

rdio/cassandra,mshuler/cassandra,dongjiaqiang/cassandra,codefollower/Cassandra-Research,iamaleksey/cassandra,ibmsoe/cassandra,HidemotoNakada/cassandra-udf,swps/cassandra,ejankan/cassandra,fengshao0907/cassandra-1,DICL/cassandra,emolsson/cassandra,jsanda/cassandra,sayanh/ViewMaintenanceCassandra,miguel0afd/cassandra-cqlMod,joesiewert/cassandra,yanbit/cassandra,instaclustr/cassandra,strapdata/cassandra,pofallon/cassandra,michaelmior/cassandra,spodkowinski/cassandra,belliottsmith/cassandra,apache/cassandra,mheffner/cassandra-1,Bj0rnen/cassandra,sedulam/CASSANDRA-12201,mike-tr-adamson/cassandra,MasahikoSawada/cassandra,nakomis/cassandra,tjake/cassandra,mkjellman/cassandra,vaibhi9/cassandra,jrwest/cassandra,tongjixianing/projects,Stratio/stratio-cassandra,mt0803/cassandra,dongjiaqiang/cassandra,xiongzheng/Cassandra-Research,aboudreault/cassandra,snazy/cassandra,sayanh/ViewMaintenanceCassandra,shookari/cassandra,shawnkumar/cstargraph,mheffner/cassandra-1,jasobrown/cassandra,strapdata/cassandra,dongjiaqiang/cassandra,nutbunnies/cassandra,sivikt/cassandra,ejankan/cassandra,weideng1/cassandra,Jollyplum/cassandra,taigetco/cassandra_read,aweisberg/cassandra,caidongyun/cassandra,leomrocha/cassandra,jbellis/cassandra,RyanMagnusson/cassandra,rackerlabs/cloudmetrics-cassandra,codefollower/Cassandra-Research,kangkot/stratio-cassandra,heiko-braun/cassandra,nitsanw/cassandra,bmel/cassandra,chaordic/cassandra,knifewine/cassandra,weideng1/cassandra,lalithsuresh/cassandra-c3,DikangGu/cassandra,hhorii/cassandra,mgmuscari/cassandra-cdh4,michaelsembwever/cassandra,ollie314/cassandra,ejankan/cassandra,guanxi55nba/db-improvement,ifesdjeen/cassandra,ptuckey/cassandra,pkdevbox/cassandra,Jaumo/cassandra,jeffjirsa/cassandra,kgreav/cassandra,JeremiahDJordan/cassandra,HidemotoNakada/cassandra-udf,rogerchina/cassandra,spodkowinski/cassandra,chbatey/cassandra-1,jasonstack/cassandra,GabrielNicolasAvellaneda/cassandra,hhorii/cassandra,rdio/cassandra,Stratio/stratio-cassandra,a-buck/cassandra,regispl/cassandra,dprguiuc/Cassandra-Wasef,wreda/cassandra,sluk3r/cassandra,Instagram/cassandra,dprguiuc/Cassandra-Wasef,clohfink/cassandra,jasobrown/cassandra,iamaleksey/cassandra,instaclustr/cassandra,heiko-braun/cassandra,AtwooTM/cassandra,Stratio/cassandra,swps/cassandra,EnigmaCurry/cassandra,ifesdjeen/cassandra,rdio/cassandra,guanxi55nba/key-value-store,yangzhe1991/cassandra,Imran-C/cassandra,ptuckey/cassandra,mambocab/cassandra,pthomaid/cassandra,pauloricardomg/cassandra,pallavi510/cassandra,DavidHerzogTU-Berlin/cassandraToRun,AtwooTM/cassandra,jeromatron/cassandra,newrelic-forks/cassandra,DavidHerzogTU-Berlin/cassandra,pallavi510/cassandra,LatencyUtils/cassandra-stress2,christian-esken/cassandra,driftx/cassandra,belliottsmith/cassandra,apache/cassandra,fengshao0907/cassandra-1,pauloricardomg/cassandra,adejanovski/cassandra,bmel/cassandra,regispl/cassandra,iburmistrov/Cassandra,driftx/cassandra,chaordic/cassandra,tongjixianing/projects,thelastpickle/cassandra,stef1927/cassandra,mheffner/cassandra-1,nlalevee/cassandra,bcoverston/apache-hosted-cassandra,modempachev4/kassandra,yukim/cassandra,likaiwalkman/cassandra,apache/cassandra,shawnkumar/cstargraph,tjake/cassandra,juiceblender/cassandra,jasonwee/cassandra,scylladb/scylla-tools-java,yukim/cassandra,blambov/cassandra,cooldoger/cassandra,DavidHerzogTU-Berlin/cassandraToRun,jrwest/cassandra,tommystendahl/cassandra,Stratio/stratio-cassandra,leomrocha/cassandra,michaelsembwever/cassandra,rackerlabs/cloudmetrics-cassandra,Bj0rnen/cassandra,yukim/cassandra,josh-mckenzie/cassandra,vramaswamy456/cassandra,regispl/cassandra,pofallon/cassandra,vaibhi9/cassandra,MasahikoSawada/cassandra,taigetco/cassandra_read,thobbs/cassandra,belliottsmith/cassandra,WorksApplications/cassandra,Instagram/cassandra,jasonwee/cassandra,shookari/cassandra,gdusbabek/cassandra,sivikt/cassandra,thobbs/cassandra,nlalevee/cassandra,shawnkumar/cstargraph,JeremiahDJordan/cassandra,DavidHerzogTU-Berlin/cassandra,blambov/cassandra,nvoron23/cassandra,rmarchei/cassandra,a-buck/cassandra,ptuckey/cassandra,strapdata/cassandra,nakomis/cassandra,fengshao0907/cassandra-1,driftx/cassandra,xiongzheng/Cassandra-Research,jeffjirsa/cassandra,Instagram/cassandra,caidongyun/cassandra,sayanh/ViewMaintenanceSupport,mkjellman/cassandra,guanxi55nba/db-improvement,rogerchina/cassandra,matthewtt/cassandra_read,szhou1234/cassandra,WorksApplications/cassandra,miguel0afd/cassandra-cqlMod,guanxi55nba/key-value-store,josh-mckenzie/cassandra,bdeggleston/cassandra,sharvanath/cassandra,likaiwalkman/cassandra,MasahikoSawada/cassandra,helena/cassandra,bcoverston/cassandra,weipinghe/cassandra,josh-mckenzie/cassandra,snazy/cassandra,clohfink/cassandra,boneill42/cassandra,jbellis/cassandra,ben-manes/cassandra,blerer/cassandra,michaelmior/cassandra,spodkowinski/cassandra,WorksApplications/cassandra,jeromatron/cassandra,sivikt/cassandra,iamaleksey/cassandra,adejanovski/cassandra,knifewine/cassandra,yonglehou/cassandra,modempachev4/kassandra,Imran-C/cassandra,nvoron23/cassandra,yonglehou/cassandra,stef1927/cassandra,swps/cassandra,wreda/cassandra,rmarchei/cassandra,spodkowinski/cassandra,weipinghe/cassandra,mike-tr-adamson/cassandra,darach/cassandra,AtwooTM/cassandra,project-zerus/cassandra,mt0803/cassandra,aureagle/cassandra,project-zerus/cassandra,thelastpickle/cassandra,jasonstack/cassandra,iburmistrov/Cassandra,rmarchei/cassandra,codefollower/Cassandra-Research,lalithsuresh/cassandra-c3,stef1927/cassandra,yanbit/cassandra,whitepages/cassandra,hhorii/cassandra,mklew/mmp,mt0803/cassandra,mklew/mmp,bdeggleston/cassandra,asias/cassandra,helena/cassandra,juiceblender/cassandra,adelapena/cassandra,jasonstack/cassandra,LatencyUtils/cassandra-stress2,DICL/cassandra,vaibhi9/cassandra,weipinghe/cassandra,pofallon/cassandra,cooldoger/cassandra,JeremiahDJordan/cassandra,hengxin/cassandra,yonglehou/cassandra,sayanh/ViewMaintenanceSupport,macintoshio/cassandra,blerer/cassandra,dkua/cassandra,jeromatron/cassandra,pcn/cassandra-1,yhnishi/cassandra,newrelic-forks/cassandra,DavidHerzogTU-Berlin/cassandraToRun,aarushi12002/cassandra,mshuler/cassandra,beobal/cassandra,instaclustr/cassandra,sriki77/cassandra,ifesdjeen/cassandra,stef1927/cassandra,ollie314/cassandra,exoscale/cassandra,tongjixianing/projects,whitepages/cassandra,scylladb/scylla-tools-java,miguel0afd/cassandra-cqlMod,aarushi12002/cassandra,chbatey/cassandra-1,helena/cassandra,macintoshio/cassandra,aweisberg/cassandra,sluk3r/cassandra,ibmsoe/cassandra,yangzhe1991/cassandra,sharvanath/cassandra,guard163/cassandra,aweisberg/cassandra,bpupadhyaya/cassandra,tommystendahl/cassandra,scylladb/scylla-tools-java,exoscale/cassandra,bcoverston/cassandra,kgreav/cassandra,mashuai/Cassandra-Research,krummas/cassandra,jkni/cassandra,fengshao0907/Cassandra-Research,kangkot/stratio-cassandra,bdeggleston/cassandra,mgmuscari/cassandra-cdh4,carlyeks/cassandra,nvoron23/cassandra,Imran-C/cassandra,pauloricardomg/cassandra,yhnishi/cassandra,christian-esken/cassandra,mambocab/cassandra,jasobrown/cassandra,joesiewert/cassandra,guard163/cassandra,sriki77/cassandra,tjake/cassandra,yukim/cassandra,fengshao0907/Cassandra-Research,aboudreault/cassandra,strapdata/cassandra,jsanda/cassandra,pcmanus/cassandra,pcn/cassandra-1,beobal/cassandra,cooldoger/cassandra,phact/cassandra,aureagle/cassandra,matthewtt/cassandra_read,scaledata/cassandra,sbtourist/cassandra,snazy/cassandra,josh-mckenzie/cassandra,adejanovski/cassandra,nakomis/cassandra,aboudreault/cassandra,kangkot/stratio-cassandra,tommystendahl/cassandra,michaelsembwever/cassandra,Jollyplum/cassandra,mklew/mmp,EnigmaCurry/cassandra,carlyeks/cassandra,ptnapoleon/cassandra,Instagram/cassandra,DikangGu/cassandra,krummas/cassandra,dkua/cassandra,DikangGu/cassandra,szhou1234/cassandra,joesiewert/cassandra,bcoverston/cassandra,qinjin/mdtc-cassandra,leomrocha/cassandra,belliottsmith/cassandra,darach/cassandra,bpupadhyaya/cassandra,pthomaid/cassandra,mashuai/Cassandra-Research,bdeggleston/cassandra,vramaswamy456/cassandra,whitepages/cassandra,GabrielNicolasAvellaneda/cassandra,DICL/cassandra,ptnapoleon/cassandra,taigetco/cassandra_read,kgreav/cassandra,apache/cassandra,dprguiuc/Cassandra-Wasef,instaclustr/cassandra,rackerlabs/cloudmetrics-cassandra,sharvanath/cassandra,gdusbabek/cassandra,exoscale/cassandra,michaelsembwever/cassandra,modempachev4/kassandra,snazy/cassandra,newrelic-forks/cassandra,mshuler/cassandra,HidemotoNakada/cassandra-udf,clohfink/cassandra,weideng1/cassandra,macintoshio/cassandra,iburmistrov/Cassandra,aureagle/cassandra,mambocab/cassandra,scylladb/scylla-tools-java,hengxin/cassandra,blambov/cassandra,shookari/cassandra,sayanh/ViewMaintenanceCassandra,dkua/cassandra,ben-manes/cassandra,yhnishi/cassandra,Stratio/cassandra,pkdevbox/cassandra,bcoverston/cassandra,adelapena/cassandra,bpupadhyaya/cassandra,LatencyUtils/cassandra-stress2,carlyeks/cassandra,mshuler/cassandra,pcmanus/cassandra,driftx/cassandra,RyanMagnusson/cassandra,tommystendahl/cassandra,mkjellman/cassandra,heiko-braun/cassandra,nutbunnies/cassandra,chaordic/cassandra,aarushi12002/cassandra,michaelmior/cassandra,darach/cassandra,iamaleksey/cassandra,blerer/cassandra,jeffjirsa/cassandra,likaiwalkman/cassandra,Jaumo/cassandra,cooldoger/cassandra,scaledata/cassandra,Stratio/stratio-cassandra,jsanda/cassandra,pthomaid/cassandra,ben-manes/cassandra,knifewine/cassandra,sedulam/CASSANDRA-12201,pallavi510/cassandra,project-zerus/cassandra,Jaumo/cassandra,ptnapoleon/cassandra,bcoverston/apache-hosted-cassandra,pcn/cassandra-1,krummas/cassandra,DavidHerzogTU-Berlin/cassandra,mgmuscari/cassandra-cdh4,GabrielNicolasAvellaneda/cassandra,phact/cassandra,matthewtt/cassandra_read,sluk3r/cassandra,juiceblender/cassandra,bcoverston/apache-hosted-cassandra,sriki77/cassandra,qinjin/mdtc-cassandra,beobal/cassandra,szhou1234/cassandra,chbatey/cassandra-1,jrwest/cassandra,qinjin/mdtc-cassandra,sbtourist/cassandra,sedulam/CASSANDRA-12201,Jollyplum/cassandra,hengxin/cassandra,ibmsoe/cassandra,xiongzheng/Cassandra-Research,vramaswamy456/cassandra,lalithsuresh/cassandra-c3,mike-tr-adamson/cassandra,szhou1234/cassandra,krummas/cassandra,asias/cassandra,jkni/cassandra,nutbunnies/cassandra,nlalevee/cassandra,fengshao0907/Cassandra-Research,thelastpickle/cassandra,guanxi55nba/db-improvement,thelastpickle/cassandra,jkni/cassandra,ollie314/cassandra,juiceblender/cassandra,pkdevbox/cassandra,sbtourist/cassandra,nitsanw/cassandra,christian-esken/cassandra,EnigmaCurry/cassandra,boneill42/cassandra,guanxi55nba/key-value-store,jbellis/cassandra,pauloricardomg/cassandra,clohfink/cassandra,WorksApplications/cassandra,bmel/cassandra,jeffjirsa/cassandra,yanbit/cassandra,wreda/cassandra,mike-tr-adamson/cassandra,blambov/cassandra,mashuai/Cassandra-Research,emolsson/cassandra,ifesdjeen/cassandra,beobal/cassandra,nitsanw/cassandra,jasobrown/cassandra,mkjellman/cassandra,thobbs/cassandra,RyanMagnusson/cassandra,asias/cassandra,aweisberg/cassandra,jrwest/cassandra,rogerchina/cassandra,Bj0rnen/cassandra,scaledata/cassandra,kgreav/cassandra,caidongyun/cassandra,jasonwee/cassandra,kangkot/stratio-cassandra,kangkot/stratio-cassandra,guard163/cassandra,tjake/cassandra,pcmanus/cassandra,adelapena/cassandra,a-buck/cassandra,Stratio/cassandra,Stratio/stratio-cassandra,boneill42/cassandra,blerer/cassandra,phact/cassandra,emolsson/cassandra,yangzhe1991/cassandra,gdusbabek/cassandra,adelapena/cassandra