Fix small query-lifespan memory leak in bulk updates.
Fix small query-lifespan memory leak in bulk updates.

When there is an identifiable REPLICA IDENTITY index on the target table,
heap_update leaks the id_attrs bitmapset.  That's not many bytes, but it
adds up over enough rows, since the code typically runs in a query-lifespan
context.  Bug introduced in commit e55704d8b, which did a rather poor job
of cloning the existing use-pattern for RelationGetIndexAttrBitmap().

Per bug #14293 from Zhou Digoal.  Back-patch to 9.4 where the bug was
introduced.

Report: <32710ff43f6d6261702d3c964f01151d695aecfb@wrigleys.postgresql.org>

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