Add missing GP_WRAP_START/END to gpdb::MakeGpPolicy.
Add missing GP_WRAP_START/END to gpdb::MakeGpPolicy.

makeGpPolicy() uses palloc(), which can throw an error, so wrappers are
needed. Also add a comment to gpdb:IsAbortRequested to explain why it
doesn't need wrappers. I suspect the missing wrappers in MakeGpPolicy()
happened because it was copy-pasted from IsAbortRequested.

lisakowen/gpdb,xinzweb/gpdb,xinzweb/gpdb,jmcatamney/gpdb,50wu/gpdb,greenplum-db/gpdb,adam8157/gpdb,ashwinstar/gpdb,50wu/gpdb,lisakowen/gpdb,lisakowen/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,adam8157/gpdb,50wu/gpdb,50wu/gpdb,xinzweb/gpdb,xinzweb/gpdb,50wu/gpdb,xinzweb/gpdb,lisakowen/gpdb,ashwinstar/gpdb,adam8157/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,lisakowen/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,50wu/gpdb,50wu/gpdb,ashwinstar/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,adam8157/gpdb,adam8157/gpdb,lisakowen/gpdb,adam8157/gpdb,50wu/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,jmcatamney/gpdb,adam8157/gpdb,ashwinstar/gpdb,lisakowen/gpdb,adam8157/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,jmcatamney/gpdb,xinzweb/gpdb,xinzweb/gpdb,lisakowen/gpdb,xinzweb/gpdb,jmcatamney/gpdb