Fix bugs in pltcl's new return_null command: it was liable to go belly up if the return datatype's input converter was at all strict, because the converter would get called on junk data when returning NULL.  Also ensure that it gives an error rather than coredumping if someone tries to use it in a trigger function.
Fix bugs in pltcl's new return_null command: it was liable to go belly up
if the return datatype's input converter was at all strict, because the
converter would get called on junk data when returning NULL.  Also
ensure that it gives an error rather than coredumping if someone tries
to use it in a trigger function.

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