Document timeofday(), mention start-of-transaction vs. current-time semantics, a few other small improvements.
Document timeofday(), mention start-of-transaction vs. current-time
semantics, a few other small improvements.

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