Improve error message for case where DROP TABLE is rejected because table has a child table.
Improve error message for case where DROP TABLE is rejected because
table has a child table.

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