Add mention of environment variable conflict with uncommenting config file variables:
Add mention of environment variable conflict with uncommenting config
file variables:

<   Another option is to allow commented values to return to their
<   default values.
>   This has to address environment variables that are then overridden
>   by config file values.  Another option is to allow commented values
>   to return to their default values.

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