Fix reduce levels
Fix reduce levels

ReduceNumberOfLevels had segmentation fault in WriteSnapshot() since we
didn't change the number of levels in VersionSet (we consider them
immutable from now on). This fixes the problem.

RyanTech/rocksdb,ryneli/rocksdb,temicai/rocksdb,geraldoandradee/rocksdb,JoeWoo/rocksdb,temicai/rocksdb,facebook/rocksdb,OverlordQ/rocksdb,bbiao/rocksdb,makelivedotnet/rocksdb,amyvmiwei/rocksdb,mbarbon/rocksdb,msb-at-yahoo/rocksdb,jalexanderqed/rocksdb,tizzybec/rocksdb,geraldoandradee/rocksdb,skunkwerks/rocksdb,SunguckLee/RocksDB,mbarbon/rocksdb,wskplho/rocksdb,wat-ze-hex/rocksdb,biddyweb/rocksdb,wenduo/rocksdb,flabby/rocksdb,lgscofield/rocksdb,virtdb/rocksdb,wenduo/rocksdb,Andymic/rocksdb,SunguckLee/RocksDB,NickCis/rocksdb,wlqGit/rocksdb,virtdb/rocksdb,jalexanderqed/rocksdb,flabby/rocksdb,makelivedotnet/rocksdb,tsheasha/rocksdb,kaschaeffer/rocksdb,hobinyoon/rocksdb,tizzybec/rocksdb,tsheasha/rocksdb,jalexanderqed/rocksdb,sorphi/rocksdb,virtdb/rocksdb,fengshao0907/rocksdb,JohnPJenkins/rocksdb,JoeWoo/rocksdb,caijieming-baidu/rocksdb,skunkwerks/rocksdb,Applied-Duality/rocksdb,rDSN-Projects/rocksdb.replicated,sorphi/rocksdb,tizzybec/rocksdb,zhangpng/rocksdb,SunguckLee/RocksDB,wenduo/rocksdb,wlqGit/rocksdb,wat-ze-hex/rocksdb,Vaisman/rocksdb,caijieming-baidu/rocksdb,siddhartharay007/rocksdb,JohnPJenkins/rocksdb,ryneli/rocksdb,makelivedotnet/rocksdb,amyvmiwei/rocksdb,tsheasha/rocksdb,facebook/rocksdb,caijieming-baidu/rocksdb,biddyweb/rocksdb,ryneli/rocksdb,virtdb/rocksdb,wlqGit/rocksdb,Andymic/rocksdb,IMCG/RcoksDB,mbarbon/rocksdb,caijieming-baidu/rocksdb,kaschaeffer/rocksdb,OverlordQ/rocksdb,facebook/rocksdb,caijieming-baidu/rocksdb,dkorolev/rocksdb,dkorolev/rocksdb,wat-ze-hex/rocksdb,JackLian/rocksdb,tsheasha/rocksdb,msb-at-yahoo/rocksdb,kaschaeffer/rocksdb,Andymic/rocksdb,hobinyoon/rocksdb,sorphi/rocksdb,tizzybec/rocksdb,bbiao/rocksdb,OverlordQ/rocksdb,flabby/rocksdb,anagav/rocksdb,tsheasha/rocksdb,wat-ze-hex/rocksdb,virtdb/rocksdb,mbarbon/rocksdb,SunguckLee/RocksDB,siddhartharay007/rocksdb,vashstorm/rocksdb,wat-ze-hex/rocksdb,JohnPJenkins/rocksdb,skunkwerks/rocksdb,norton/rocksdb,skunkwerks/rocksdb,makelivedotnet/rocksdb,SunguckLee/RocksDB,biddyweb/rocksdb,biddyweb/rocksdb,siddhartharay007/rocksdb,alihalabyah/rocksdb,JohnPJenkins/rocksdb,Applied-Duality/rocksdb,zhangpng/rocksdb,dkorolev/rocksdb,temicai/rocksdb,ylong/rocksdb,alihalabyah/rocksdb,JackLian/rocksdb,bbiao/rocksdb,NickCis/rocksdb,tschottdorf/rocksdb,zhangpng/rocksdb,rDSN-Projects/rocksdb.replicated,JackLian/rocksdb,vmx/rocksdb,bbiao/rocksdb,zhangpng/rocksdb,luckywhu/rocksdb,ryneli/rocksdb,wenduo/rocksdb,vashstorm/rocksdb,virtdb/rocksdb,amyvmiwei/rocksdb,makelivedotnet/rocksdb,ryneli/rocksdb,IMCG/RcoksDB,wenduo/rocksdb,RyanTech/rocksdb,OverlordQ/rocksdb,Applied-Duality/rocksdb,temicai/rocksdb,norton/rocksdb,wlqGit/rocksdb,JohnPJenkins/rocksdb,kaschaeffer/rocksdb,JoeWoo/rocksdb,mbarbon/rocksdb,temicai/rocksdb,geraldoandradee/rocksdb,wskplho/rocksdb,jalexanderqed/rocksdb,norton/rocksdb,siddhartharay007/rocksdb,flabby/rocksdb,ylong/rocksdb,facebook/rocksdb,JoeWoo/rocksdb,rDSN-Projects/rocksdb.replicated,geraldoandradee/rocksdb,Applied-Duality/rocksdb,tschottdorf/rocksdb,wskplho/rocksdb,IMCG/RcoksDB,NickCis/rocksdb,SunguckLee/RocksDB,luckywhu/rocksdb,rDSN-Projects/rocksdb.replicated,Vaisman/rocksdb,OverlordQ/rocksdb,ylong/rocksdb,luckywhu/rocksdb,siddhartharay007/rocksdb,wlqGit/rocksdb,alihalabyah/rocksdb,rDSN-Projects/rocksdb.replicated,Applied-Duality/rocksdb,Andymic/rocksdb,ylong/rocksdb,tizzybec/rocksdb,caijieming-baidu/rocksdb,NickCis/rocksdb,dkorolev/rocksdb,caijieming-baidu/rocksdb,biddyweb/rocksdb,alihalabyah/rocksdb,hobinyoon/rocksdb,Andymic/rocksdb,skunkwerks/rocksdb,bbiao/rocksdb,vmx/rocksdb,norton/rocksdb,vmx/rocksdb,OverlordQ/rocksdb,NickCis/rocksdb,alihalabyah/rocksdb,JoeWoo/rocksdb,wskplho/rocksdb,siddhartharay007/rocksdb,SunguckLee/RocksDB,jalexanderqed/rocksdb,hobinyoon/rocksdb,mbarbon/rocksdb,makelivedotnet/rocksdb,hobinyoon/rocksdb,skunkwerks/rocksdb,wat-ze-hex/rocksdb,zhangpng/rocksdb,geraldoandradee/rocksdb,norton/rocksdb,amyvmiwei/rocksdb,bbiao/rocksdb,anagav/rocksdb,JohnPJenkins/rocksdb,hobinyoon/rocksdb,luckywhu/rocksdb,norton/rocksdb,lgscofield/rocksdb,Andymic/rocksdb,wskplho/rocksdb,flabby/rocksdb,lgscofield/rocksdb,SunguckLee/RocksDB,tschottdorf/rocksdb,Applied-Duality/rocksdb,msb-at-yahoo/rocksdb,vmx/rocksdb,wenduo/rocksdb,wskplho/rocksdb,tschottdorf/rocksdb,virtdb/rocksdb,NickCis/rocksdb,ryneli/rocksdb,flabby/rocksdb,JackLian/rocksdb,wenduo/rocksdb,facebook/rocksdb,IMCG/RcoksDB,ylong/rocksdb,JoeWoo/rocksdb,sorphi/rocksdb,temicai/rocksdb,JoeWoo/rocksdb,norton/rocksdb,temicai/rocksdb,tsheasha/rocksdb,tizzybec/rocksdb,skunkwerks/rocksdb,JackLian/rocksdb,vmx/rocksdb,vashstorm/rocksdb,anagav/rocksdb,wlqGit/rocksdb,anagav/rocksdb,zhangpng/rocksdb,vmx/rocksdb,vashstorm/rocksdb,JackLian/rocksdb,IMCG/RcoksDB,dkorolev/rocksdb,jalexanderqed/rocksdb,dkorolev/rocksdb,vashstorm/rocksdb,fengshao0907/rocksdb,geraldoandradee/rocksdb,JohnPJenkins/rocksdb,vashstorm/rocksdb,Vaisman/rocksdb,vmx/rocksdb,tschottdorf/rocksdb,rDSN-Projects/rocksdb.replicated,msb-at-yahoo/rocksdb,anagav/rocksdb,sorphi/rocksdb,NickCis/rocksdb,IMCG/RcoksDB,siddhartharay007/rocksdb,Applied-Duality/rocksdb,wlqGit/rocksdb,lgscofield/rocksdb,lgscofield/rocksdb,facebook/rocksdb,tsheasha/rocksdb,fengshao0907/rocksdb,wskplho/rocksdb,JackLian/rocksdb,hobinyoon/rocksdb,fengshao0907/rocksdb,RyanTech/rocksdb,ryneli/rocksdb,lgscofield/rocksdb,Andymic/rocksdb,msb-at-yahoo/rocksdb,Vaisman/rocksdb,RyanTech/rocksdb,kaschaeffer/rocksdb,Vaisman/rocksdb,fengshao0907/rocksdb,alihalabyah/rocksdb,anagav/rocksdb,rDSN-Projects/rocksdb.replicated,RyanTech/rocksdb,amyvmiwei/rocksdb,tsheasha/rocksdb,facebook/rocksdb,ylong/rocksdb,flabby/rocksdb,norton/rocksdb,OverlordQ/rocksdb,amyvmiwei/rocksdb,geraldoandradee/rocksdb,wat-ze-hex/rocksdb,biddyweb/rocksdb,RyanTech/rocksdb,Andymic/rocksdb,mbarbon/rocksdb,vashstorm/rocksdb,RyanTech/rocksdb,fengshao0907/rocksdb,IMCG/RcoksDB,Vaisman/rocksdb,dkorolev/rocksdb,kaschaeffer/rocksdb,luckywhu/rocksdb,bbiao/rocksdb,zhangpng/rocksdb,wenduo/rocksdb,lgscofield/rocksdb,jalexanderqed/rocksdb,Vaisman/rocksdb,alihalabyah/rocksdb,fengshao0907/rocksdb,kaschaeffer/rocksdb,luckywhu/rocksdb,tizzybec/rocksdb,amyvmiwei/rocksdb,luckywhu/rocksdb,facebook/rocksdb,sorphi/rocksdb,anagav/rocksdb,sorphi/rocksdb,msb-at-yahoo/rocksdb,makelivedotnet/rocksdb,tschottdorf/rocksdb,vmx/rocksdb,hobinyoon/rocksdb,wat-ze-hex/rocksdb,bbiao/rocksdb,ylong/rocksdb,biddyweb/rocksdb