Allow extract() to accept the same field selectors as date_part(), not just the ones specified by SQL.
Allow extract() to accept the same field selectors as date_part(), not just
the ones specified by SQL.

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