Fix assign_session_authorization() to not be confused by all-numeric user names.  Per recent reports.
Fix assign_session_authorization() to not be confused by all-numeric
user names.  Per recent reports.

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