Un-break EXPLAIN for Append plans. I messed this up a few days ago while

adding the ModifyTable node type --- I had been thinking ModifyTable should
replace Append as a special case in push_plan(), but actually both of them
have to be special-cased.

src/backend/utils/adt/ruleutils.c

@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/ruleutils.c,v 1.312 2009/10/28 17:36:50 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/ruleutils.c,v 1.313 2009/10/28 18:51:56 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -3370,11 +3370,16 @@ static void
 push_plan(deparse_namespace *dpns, Plan *subplan)
 {
 	/*
-	 * We special-case ModifyTable to pretend that the first child plan is the
-	 * OUTER referent; otherwise normal.  This is to support RETURNING lists
-	 * containing references to non-target relations.
+	 * We special-case Append to pretend that the first child plan is the
+	 * OUTER referent; we have to interpret OUTER Vars in the Append's tlist
+	 * according to one of the children, and the first one is the most
+	 * natural choice.  Likewise special-case ModifyTable to pretend that the
+	 * first child plan is the OUTER referent; this is to support RETURNING
+	 * lists containing references to non-target relations.
 	 */
-	if (IsA(subplan, ModifyTable))
+	if (IsA(subplan, Append))
+		dpns->outer_plan = (Plan *) linitial(((Append *) subplan)->appendplans);
+	else if (IsA(subplan, ModifyTable))
 		dpns->outer_plan = (Plan *) linitial(((ModifyTable *) subplan)->plans);
 	else
 		dpns->outer_plan = outerPlan(subplan);