fix bug for external sorting
fix bug for external sorting

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