Don't cache per-group context across the whole query in orderedsetaggs.c.
Don't cache per-group context across the whole query in orderedsetaggs.c.

Although nodeAgg.c currently uses the same per-group memory context for
all groups of a query, that might change in future.  Avoid assuming it.
This costs us an extra AggCheckCallContext() call per group, but that's
pretty cheap and is probably good from a safety standpoint anyway.

Back-patch to 9.4 in case any third-party code copies this logic.

Andrew Gierth

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