fix compiler error on OS X. Subtracting two unsigned ints will never be less than 0
fix compiler error on OS X. Subtracting two unsigned ints will never be less than 0

foyzur/gpdb,Quikling/gpdb,CraigHarris/gpdb,kaknikhil/gpdb,adam8157/gpdb,foyzur/gpdb,chrishajas/gpdb,ahachete/gpdb,rubikloud/gpdb,atris/gpdb,lintzc/gpdb,lpetrov-pivotal/gpdb,jmcatamney/gpdb,foyzur/gpdb,tangp3/gpdb,royc1/gpdb,50wu/gpdb,Chibin/gpdb,atris/gpdb,xuegang/gpdb,zaksoup/gpdb,rvs/gpdb,jmcatamney/gpdb,randomtask1155/gpdb,royc1/gpdb,adam8157/gpdb,lintzc/gpdb,Quikling/gpdb,zaksoup/gpdb,rubikloud/gpdb,adam8157/gpdb,greenplum-db/gpdb,yuanzhao/gpdb,lisakowen/gpdb,greenplum-db/gpdb,chrishajas/gpdb,kaknikhil/gpdb,kaknikhil/gpdb,Quikling/gpdb,cjcjameson/gpdb,xinzweb/gpdb,lpetrov-pivotal/gpdb,randomtask1155/gpdb,cjcjameson/gpdb,lpetrov-pivotal/gpdb,rubikloud/gpdb,50wu/gpdb,jmcatamney/gpdb,lisakowen/gpdb,tangp3/gpdb,rubikloud/gpdb,lisakowen/gpdb,yuanzhao/gpdb,kaknikhil/gpdb,xinzweb/gpdb,lisakowen/gpdb,greenplum-db/gpdb,ahachete/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,xuegang/gpdb,xuegang/gpdb,yuanzhao/gpdb,lpetrov-pivotal/gpdb,randomtask1155/gpdb,atris/gpdb,lintzc/gpdb,foyzur/gpdb,ahachete/gpdb,50wu/gpdb,Chibin/gpdb,0x0FFF/gpdb,lisakowen/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,Chibin/gpdb,lpetrov-pivotal/gpdb,CraigHarris/gpdb,kaknikhil/gpdb,lintzc/gpdb,cjcjameson/gpdb,foyzur/gpdb,xuegang/gpdb,ahachete/gpdb,rubikloud/gpdb,edespino/gpdb,chrishajas/gpdb,Quikling/gpdb,zaksoup/gpdb,xinzweb/gpdb,rubikloud/gpdb,yuanzhao/gpdb,royc1/gpdb,foyzur/gpdb,zaksoup/gpdb,janebeckman/gpdb,royc1/gpdb,ahachete/gpdb,ahachete/gpdb,lpetrov-pivotal/gpdb,lintzc/gpdb,CraigHarris/gpdb,atris/gpdb,Chibin/gpdb,tangp3/gpdb,kaknikhil/gpdb,greenplum-db/gpdb,ahachete/gpdb,Quikling/gpdb,Quikling/gpdb,kaknikhil/gpdb,atris/gpdb,0x0FFF/gpdb,ashwinstar/gpdb,chrishajas/gpdb,chrishajas/gpdb,rvs/gpdb,CraigHarris/gpdb,lisakowen/gpdb,yuanzhao/gpdb,Chibin/gpdb,janebeckman/gpdb,50wu/gpdb,xuegang/gpdb,royc1/gpdb,cjcjameson/gpdb,cjcjameson/gpdb,0x0FFF/gpdb,CraigHarris/gpdb,CraigHarris/gpdb,tangp3/gpdb,janebeckman/gpdb,rvs/gpdb,xinzweb/gpdb,xuegang/gpdb,cjcjameson/gpdb,janebeckman/gpdb,rvs/gpdb,adam8157/gpdb,randomtask1155/gpdb,kaknikhil/gpdb,0x0FFF/gpdb,yuanzhao/gpdb,ashwinstar/gpdb,yuanzhao/gpdb,edespino/gpdb,royc1/gpdb,edespino/gpdb,randomtask1155/gpdb,50wu/gpdb,greenplum-db/gpdb,edespino/gpdb,rvs/gpdb,cjcjameson/gpdb,Quikling/gpdb,janebeckman/gpdb,yuanzhao/gpdb,lisakowen/gpdb,atris/gpdb,CraigHarris/gpdb,xinzweb/gpdb,kaknikhil/gpdb,adam8157/gpdb,Quikling/gpdb,CraigHarris/gpdb,0x0FFF/gpdb,xinzweb/gpdb,50wu/gpdb,atris/gpdb,rvs/gpdb,zaksoup/gpdb,xinzweb/gpdb,lisakowen/gpdb,yuanzhao/gpdb,edespino/gpdb,0x0FFF/gpdb,ahachete/gpdb,ashwinstar/gpdb,edespino/gpdb,rubikloud/gpdb,atris/gpdb,edespino/gpdb,randomtask1155/gpdb,cjcjameson/gpdb,rvs/gpdb,0x0FFF/gpdb,Chibin/gpdb,cjcjameson/gpdb,Chibin/gpdb,ashwinstar/gpdb,royc1/gpdb,yuanzhao/gpdb,lintzc/gpdb,xinzweb/gpdb,rvs/gpdb,Chibin/gpdb,0x0FFF/gpdb,adam8157/gpdb,zaksoup/gpdb,foyzur/gpdb,greenplum-db/gpdb,randomtask1155/gpdb,50wu/gpdb,ashwinstar/gpdb,ashwinstar/gpdb,adam8157/gpdb,Quikling/gpdb,randomtask1155/gpdb,janebeckman/gpdb,ashwinstar/gpdb,CraigHarris/gpdb,janebeckman/gpdb,jmcatamney/gpdb,tangp3/gpdb,edespino/gpdb,kaknikhil/gpdb,royc1/gpdb,lintzc/gpdb,Quikling/gpdb,lintzc/gpdb,janebeckman/gpdb,lpetrov-pivotal/gpdb,chrishajas/gpdb,tangp3/gpdb,zaksoup/gpdb,edespino/gpdb,janebeckman/gpdb,cjcjameson/gpdb,tangp3/gpdb,Chibin/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,chrishajas/gpdb,foyzur/gpdb,rvs/gpdb,edespino/gpdb,zaksoup/gpdb,adam8157/gpdb,xuegang/gpdb,xuegang/gpdb,greenplum-db/gpdb,Chibin/gpdb,lintzc/gpdb,janebeckman/gpdb,lpetrov-pivotal/gpdb,rvs/gpdb,tangp3/gpdb,xuegang/gpdb,chrishajas/gpdb,rubikloud/gpdb,50wu/gpdb