Repair RI trigger visibility problems (this time for sure ;-)) per recent

discussion on pgsql-hackers: in READ COMMITTED mode we just have to force
a QuerySnapshot update in the trigger, but in SERIALIZABLE mode we have
to run the scan under a current snapshot and then complain if any rows
would be updated/deleted that are not visible in the transaction snapshot.

src/backend/commands/async.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/commands/async.c,v 1.100 2003/09/15 23:33:39 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/commands/async.c,v 1.101 2003/10/01 21:30:52 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -537,7 +537,7 @@ AtCommit_Notify(void)
 				 */
 				result = heap_update(lRel, &lTuple->t_self, rTuple,
 									 &ctid,
-									 GetCurrentCommandId(),
+									 GetCurrentCommandId(), SnapshotAny,
 									 false /* no wait for commit */);
 				switch (result)
 				{