Put back copyObject() call I removed in a fit of brain fade. This one

is still needed despite cleanups in setrefs.c, because the point is to
let the inserted Result node compute a different tlist than its input
node does.  Per example from Jeremy Drake.

src/backend/optimizer/plan/createplan.c

@@ -10,7 +10,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/createplan.c,v 1.226 2007/02/22 22:00:24 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/createplan.c,v 1.227 2007/02/25 17:44:01 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -2740,7 +2740,11 @@ make_sort_from_pathkeys(PlannerInfo *root, Plan *lefttree, List *pathkeys)
 			 * Do we need to insert a Result node?
 			 */
 			if (!is_projection_capable_plan(lefttree))
+			{
+				/* copy needed so we don't modify input's tlist below */
+				tlist = copyObject(tlist);
 				lefttree = (Plan *) make_result(root, tlist, NULL, lefttree);
+			}
 
 			/*
 			 * Add resjunk entry to input's tlist