Mention that some psql environment variables come from libpq and note more variables can be found in the libpq manual section.
Mention that some psql environment variables come from libpq and note
more variables can be found in the libpq manual section.

Mention .pgpass in the psql manual page section dealing with connection
parameters and point to the libpq section for more details.

Backpatch to 8.0.X.

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