Fix up gcc warnings, improve comments.
Fix up gcc warnings, improve comments.

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