Add INSERT/UPDATE/DELETE RETURNING, with basic docs and regression tests.

plpgsql support to come later.  Along the way, convert execMain's
SELECT INTO support into a DestReceiver, in order to eliminate some ugly
special cases.

Jonah Harris and Tom Lane

src/include/optimizer/planmain.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/optimizer/planmain.h,v 1.94 2006/07/26 00:34:48 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/optimizer/planmain.h,v 1.95 2006/08/12 02:52:06 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -80,6 +80,9 @@ extern void process_implied_equality(PlannerInfo *root,
  * prototypes for plan/setrefs.c
  */
 extern Plan *set_plan_references(Plan *plan, List *rtable);
+extern List *set_returning_clause_references(List *rlist,
+								Plan *topplan,
+								Index resultRelation);
 extern void fix_opfuncids(Node *node);
 extern void set_opfuncid(OpExpr *opexpr);