Issue a WARNING for external tables with too many URIs
Issue a WARNING for external tables with too many URIs

External tables with protocols file or http which specify more URIs
than segments won't be allowed to query until the cluster has been
extended. Rather than silently allow creation, issue a warning and
hint to the user to assist troubleshooting. Writable tables error
out for the same problem but avoiding to change behavior this late
in the release cycle seems like a good idea.

rvs/gpdb,Chibin/gpdb,edespino/gpdb,Chibin/gpdb,cjcjameson/gpdb,xinzweb/gpdb,janebeckman/gpdb,adam8157/gpdb,cjcjameson/gpdb,kaknikhil/gpdb,Chibin/gpdb,edespino/gpdb,kaknikhil/gpdb,edespino/gpdb,xinzweb/gpdb,jmcatamney/gpdb,adam8157/gpdb,rvs/gpdb,lisakowen/gpdb,Chibin/gpdb,xinzweb/gpdb,kaknikhil/gpdb,50wu/gpdb,Chibin/gpdb,lintzc/gpdb,Chibin/gpdb,lisakowen/gpdb,rvs/gpdb,lintzc/gpdb,xinzweb/gpdb,Quikling/gpdb,ashwinstar/gpdb,jmcatamney/gpdb,rvs/gpdb,ashwinstar/gpdb,Chibin/gpdb,lisakowen/gpdb,cjcjameson/gpdb,janebeckman/gpdb,yuanzhao/gpdb,edespino/gpdb,rvs/gpdb,jmcatamney/gpdb,kaknikhil/gpdb,janebeckman/gpdb,Quikling/gpdb,ashwinstar/gpdb,ashwinstar/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,yuanzhao/gpdb,xinzweb/gpdb,kaknikhil/gpdb,adam8157/gpdb,greenplum-db/gpdb,kaknikhil/gpdb,cjcjameson/gpdb,50wu/gpdb,yuanzhao/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,cjcjameson/gpdb,lisakowen/gpdb,Quikling/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,edespino/gpdb,lintzc/gpdb,lisakowen/gpdb,Quikling/gpdb,rvs/gpdb,lintzc/gpdb,lintzc/gpdb,lisakowen/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,Quikling/gpdb,Quikling/gpdb,cjcjameson/gpdb,lintzc/gpdb,yuanzhao/gpdb,edespino/gpdb,adam8157/gpdb,edespino/gpdb,adam8157/gpdb,yuanzhao/gpdb,lintzc/gpdb,rvs/gpdb,lintzc/gpdb,janebeckman/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,xinzweb/gpdb,kaknikhil/gpdb,Chibin/gpdb,cjcjameson/gpdb,50wu/gpdb,kaknikhil/gpdb,adam8157/gpdb,cjcjameson/gpdb,Quikling/gpdb,rvs/gpdb,kaknikhil/gpdb,yuanzhao/gpdb,xinzweb/gpdb,janebeckman/gpdb,Chibin/gpdb,janebeckman/gpdb,jmcatamney/gpdb,cjcjameson/gpdb,janebeckman/gpdb,janebeckman/gpdb,Quikling/gpdb,yuanzhao/gpdb,adam8157/gpdb,50wu/gpdb,Quikling/gpdb,rvs/gpdb,janebeckman/gpdb,greenplum-db/gpdb,50wu/gpdb,greenplum-db/gpdb,yuanzhao/gpdb,edespino/gpdb,ashwinstar/gpdb,ashwinstar/gpdb,yuanzhao/gpdb,lisakowen/gpdb,Chibin/gpdb,janebeckman/gpdb,yuanzhao/gpdb,50wu/gpdb,50wu/gpdb,rvs/gpdb,cjcjameson/gpdb,adam8157/gpdb,50wu/gpdb,xinzweb/gpdb,edespino/gpdb,kaknikhil/gpdb,lisakowen/gpdb,edespino/gpdb,Quikling/gpdb,lintzc/gpdb