Improve descriptions of date/time functions.
Improve descriptions of date/time functions.

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