Modify the relcache to record the temp status of both local and nonlocal

temp relations; this is no more expensive than before, now that we have
pg_class.relistemp.  Insert tests into bufmgr.c to prevent attempting
to fetch pages from nonlocal temp relations.  This provides a low-level
defense against bugs-of-omission allowing temp pages to be loaded into shared
buffers, as in the contrib/pgstattuple problem reported by Stuart Bishop.
While at it, tweak a bunch of places to use new relcache tests (instead of
expensive probes into pg_namespace) to detect local or nonlocal temp tables.

src/backend/optimizer/prep/prepunion.c

@@ -22,7 +22,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/prep/prepunion.c,v 1.167 2009/03/05 17:30:29 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/prep/prepunion.c,v 1.168 2009/03/31 22:12:48 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1258,21 +1258,23 @@ expand_inherited_rtentry(PlannerInfo *root, RangeTblEntry *rte, Index rti)
 		Index		childRTindex;
 		AppendRelInfo *appinfo;
 
+		/* Open rel, acquire the appropriate lock type */
+		if (childOID != parentOID)
+			newrelation = heap_open(childOID, lockmode);
+		else
+			newrelation = oldrelation;
+
 		/*
 		 * It is possible that the parent table has children that are temp
 		 * tables of other backends.  We cannot safely access such tables
 		 * (because of buffering issues), and the best thing to do seems to be
 		 * to silently ignore them.
 		 */
-		if (childOID != parentOID &&
-			isOtherTempNamespace(get_rel_namespace(childOID)))
+		if (childOID != parentOID && RELATION_IS_OTHER_TEMP(newrelation))
+		{
+			heap_close(newrelation, lockmode);
 			continue;
-
-		/* Open rel, acquire the appropriate lock type */
-		if (childOID != parentOID)
-			newrelation = heap_open(childOID, lockmode);
-		else
-			newrelation = oldrelation;
+		}
 
 		/*
 		 * Build an RTE for the child, and attach to query's rangetable list.