Fix AfterTriggerSaveEvent to use a test and elog, not just Assert, to check

that it's called within an AfterTriggerBeginQuery/AfterTriggerEndQuery pair.
The RI cascade triggers suppress that overhead on the assumption that they
are always run non-deferred, so it's possible to violate the condition if
someone mistakenly changes pg_trigger to mark such a trigger deferred.
We don't really care about supporting that, but throwing an error instead
of crashing seems desirable.  Per report from Marcelo Costa.

src/backend/commands/trigger.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/trigger.c,v 1.227.2.2 2008/12/13 02:00:29 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/trigger.c,v 1.227.2.3 2009/10/27 20:14:39 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -3606,8 +3606,15 @@ AfterTriggerSaveEvent(ResultRelInfo *relinfo, int event, bool row_trigger,
 	ItemPointerData oldctid;
 	ItemPointerData newctid;
 
+	/*
+	 * Check state.  We use normal tests not Asserts because it is possible
+	 * to reach here in the wrong state given misconfigured RI triggers,
+	 * in particular deferring a cascade action trigger.
+	 */
 	if (afterTriggers == NULL)
 		elog(ERROR, "AfterTriggerSaveEvent() called outside of transaction");
+	if (afterTriggers->query_depth < 0)
+		elog(ERROR, "AfterTriggerSaveEvent() called outside of query");
 
 	/*
 	 * Get the CTID's of OLD and NEW