Don't crash if subquery appears multiple times in jointree.  This should not happen anyway, but let's try not to get completely confused if it does (due to rewriter bugs or whatever).
Don't crash if subquery appears multiple times in jointree.  This should
not happen anyway, but let's try not to get completely confused if it does
(due to rewriter bugs or whatever).

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