Add mention of rules/triggers:
Add mention of rules/triggers:

> * Add MERGE command that does UPDATE, or on failure, INSERT (rules, triggers?)

atris/gpdb,chrishajas/gpdb,techdragon/Postgres-XL,chrishajas/gpdb,cjcjameson/gpdb,royc1/gpdb,royc1/gpdb,tpostgres-projects/tPostgres,janebeckman/gpdb,50wu/gpdb,0x0FFF/gpdb,jmcatamney/gpdb,tangp3/gpdb,Quikling/gpdb,xuegang/gpdb,xinzweb/gpdb,randomtask1155/gpdb,xinzweb/gpdb,zaksoup/gpdb,chrishajas/gpdb,yuanzhao/gpdb,oberstet/postgres-xl,Quikling/gpdb,edespino/gpdb,zaksoup/gpdb,Quikling/gpdb,ashwinstar/gpdb,ahachete/gpdb,yuanzhao/gpdb,snaga/postgres-xl,atris/gpdb,adam8157/gpdb,chrishajas/gpdb,royc1/gpdb,cjcjameson/gpdb,janebeckman/gpdb,ovr/postgres-xl,jmcatamney/gpdb,pavanvd/postgres-xl,edespino/gpdb,zeroae/postgres-xl,tpostgres-projects/tPostgres,rvs/gpdb,lpetrov-pivotal/gpdb,rvs/gpdb,lintzc/gpdb,CraigHarris/gpdb,foyzur/gpdb,janebeckman/gpdb,greenplum-db/gpdb,zaksoup/gpdb,lisakowen/gpdb,postmind-net/postgres-xl,CraigHarris/gpdb,edespino/gpdb,CraigHarris/gpdb,lpetrov-pivotal/gpdb,kaknikhil/gpdb,ashwinstar/gpdb,oberstet/postgres-xl,Quikling/gpdb,ahachete/gpdb,rubikloud/gpdb,lintzc/gpdb,tangp3/gpdb,atris/gpdb,kmjungersen/PostgresXL,xuegang/gpdb,cjcjameson/gpdb,greenplum-db/gpdb,CraigHarris/gpdb,kaknikhil/gpdb,50wu/gpdb,Chibin/gpdb,edespino/gpdb,Postgres-XL/Postgres-XL,oberstet/postgres-xl,foyzur/gpdb,royc1/gpdb,janebeckman/gpdb,xuegang/gpdb,janebeckman/gpdb,tpostgres-projects/tPostgres,Postgres-XL/Postgres-XL,yuanzhao/gpdb,lisakowen/gpdb,xinzweb/gpdb,arcivanov/postgres-xl,randomtask1155/gpdb,cjcjameson/gpdb,CraigHarris/gpdb,0x0FFF/gpdb,rubikloud/gpdb,Postgres-XL/Postgres-XL,lisakowen/gpdb,techdragon/Postgres-XL,jmcatamney/gpdb,zaksoup/gpdb,50wu/gpdb,kmjungersen/PostgresXL,royc1/gpdb,janebeckman/gpdb,xinzweb/gpdb,xuegang/gpdb,ahachete/gpdb,rvs/gpdb,yuanzhao/gpdb,foyzur/gpdb,adam8157/gpdb,postmind-net/postgres-xl,Chibin/gpdb,foyzur/gpdb,greenplum-db/gpdb,techdragon/Postgres-XL,Chibin/gpdb,greenplum-db/gpdb,CraigHarris/gpdb,janebeckman/gpdb,cjcjameson/gpdb,pavanvd/postgres-xl,randomtask1155/gpdb,yuanzhao/gpdb,randomtask1155/gpdb,kaknikhil/gpdb,postmind-net/postgres-xl,ashwinstar/gpdb,Quikling/gpdb,cjcjameson/gpdb,50wu/gpdb,arcivanov/postgres-xl,pavanvd/postgres-xl,yuanzhao/gpdb,rubikloud/gpdb,atris/gpdb,lpetrov-pivotal/gpdb,0x0FFF/gpdb,xuegang/gpdb,0x0FFF/gpdb,royc1/gpdb,tangp3/gpdb,ovr/postgres-xl,lintzc/gpdb,rubikloud/gpdb,lintzc/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,Chibin/gpdb,Chibin/gpdb,pavanvd/postgres-xl,50wu/gpdb,Chibin/gpdb,kmjungersen/PostgresXL,arcivanov/postgres-xl,yazun/postgres-xl,lpetrov-pivotal/gpdb,kaknikhil/gpdb,Chibin/gpdb,postmind-net/postgres-xl,rvs/gpdb,adam8157/gpdb,cjcjameson/gpdb,ashwinstar/gpdb,tangp3/gpdb,zeroae/postgres-xl,jmcatamney/gpdb,ahachete/gpdb,cjcjameson/gpdb,Postgres-XL/Postgres-XL,ahachete/gpdb,lpetrov-pivotal/gpdb,adam8157/gpdb,yazun/postgres-xl,ovr/postgres-xl,ahachete/gpdb,yazun/postgres-xl,atris/gpdb,ahachete/gpdb,royc1/gpdb,lpetrov-pivotal/gpdb,yazun/postgres-xl,lisakowen/gpdb,50wu/gpdb,Quikling/gpdb,foyzur/gpdb,snaga/postgres-xl,ashwinstar/gpdb,zaksoup/gpdb,lisakowen/gpdb,postmind-net/postgres-xl,xinzweb/gpdb,rvs/gpdb,kaknikhil/gpdb,edespino/gpdb,0x0FFF/gpdb,randomtask1155/gpdb,kmjungersen/PostgresXL,yuanzhao/gpdb,lisakowen/gpdb,Chibin/gpdb,Quikling/gpdb,50wu/gpdb,rvs/gpdb,foyzur/gpdb,xinzweb/gpdb,tpostgres-projects/tPostgres,CraigHarris/gpdb,chrishajas/gpdb,oberstet/postgres-xl,yuanzhao/gpdb,ovr/postgres-xl,lisakowen/gpdb,xinzweb/gpdb,Quikling/gpdb,rubikloud/gpdb,randomtask1155/gpdb,0x0FFF/gpdb,cjcjameson/gpdb,adam8157/gpdb,CraigHarris/gpdb,greenplum-db/gpdb,edespino/gpdb,greenplum-db/gpdb,techdragon/Postgres-XL,zeroae/postgres-xl,CraigHarris/gpdb,zaksoup/gpdb,kaknikhil/gpdb,atris/gpdb,snaga/postgres-xl,Chibin/gpdb,rubikloud/gpdb,yuanzhao/gpdb,lintzc/gpdb,xuegang/gpdb,zaksoup/gpdb,jmcatamney/gpdb,zeroae/postgres-xl,atris/gpdb,chrishajas/gpdb,lintzc/gpdb,kmjungersen/PostgresXL,arcivanov/postgres-xl,adam8157/gpdb,zeroae/postgres-xl,royc1/gpdb,tpostgres-projects/tPostgres,lintzc/gpdb,rvs/gpdb,adam8157/gpdb,rvs/gpdb,adam8157/gpdb,lisakowen/gpdb,kaknikhil/gpdb,xuegang/gpdb,xuegang/gpdb,ashwinstar/gpdb,lpetrov-pivotal/gpdb,pavanvd/postgres-xl,oberstet/postgres-xl,edespino/gpdb,50wu/gpdb,chrishajas/gpdb,Quikling/gpdb,techdragon/Postgres-XL,Chibin/gpdb,rvs/gpdb,ashwinstar/gpdb,yazun/postgres-xl,randomtask1155/gpdb,janebeckman/gpdb,edespino/gpdb,lintzc/gpdb,rvs/gpdb,cjcjameson/gpdb,tangp3/gpdb,0x0FFF/gpdb,tangp3/gpdb,ashwinstar/gpdb,ovr/postgres-xl,foyzur/gpdb,lpetrov-pivotal/gpdb,jmcatamney/gpdb,ahachete/gpdb,Postgres-XL/Postgres-XL,jmcatamney/gpdb,arcivanov/postgres-xl,tangp3/gpdb,rubikloud/gpdb,yuanzhao/gpdb,zaksoup/gpdb,edespino/gpdb,xinzweb/gpdb,janebeckman/gpdb,xuegang/gpdb,edespino/gpdb,kaknikhil/gpdb,snaga/postgres-xl,rubikloud/gpdb,kaknikhil/gpdb,kaknikhil/gpdb,Quikling/gpdb,snaga/postgres-xl,greenplum-db/gpdb,arcivanov/postgres-xl,foyzur/gpdb,0x0FFF/gpdb,atris/gpdb,chrishajas/gpdb,lintzc/gpdb,janebeckman/gpdb,tangp3/gpdb,randomtask1155/gpdb