Update description of timestamp types for 7.3 implementation.
Update description of timestamp types for 7.3 implementation.

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