Recognize that IN subqueries return already-unique results if they use UNION/INTERSECT/EXCEPT (without ALL).  This adds on to the previous optimization for subqueries using DISTINCT.
Recognize that IN subqueries return already-unique results if they use
UNION/INTERSECT/EXCEPT (without ALL).  This adds on to the previous
optimization for subqueries using DISTINCT.

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