Repair oversight in 8.2 change that improved the handling of "pseudoconstant"

WHERE clauses.  createplan.c is now willing to stick a gating Result node
almost anywhere in the plan tree, and in particular one can wind up directly
underneath a MergeJoin node.  This means it had better be willing to handle
Mark/Restore.  Fortunately, that's trivial in such cases, since we can just
pass off the call to the input node (which the planner has previously ensured
can handle Mark/Restore).  Per report from Phil Frost.

src/backend/executor/execAmi.c

@@ -6,7 +6,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- *	$PostgreSQL: pgsql/src/backend/executor/execAmi.c,v 1.90 2007/01/05 22:19:27 momjian Exp $
+ *	$PostgreSQL: pgsql/src/backend/executor/execAmi.c,v 1.91 2007/02/15 03:07:13 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -243,6 +243,10 @@ ExecMarkPos(PlanState *node)
 			ExecSortMarkPos((SortState *) node);
 			break;
 
+		case T_ResultState:
+			ExecResultMarkPos((ResultState *) node);
+			break;
+
 		default:
 			/* don't make hard error unless caller asks to restore... */
 			elog(DEBUG2, "unrecognized node type: %d", (int) nodeTag(node));
@@ -296,6 +300,10 @@ ExecRestrPos(PlanState *node)
 			ExecSortRestrPos((SortState *) node);
 			break;
 
+		case T_ResultState:
+			ExecResultRestrPos((ResultState *) node);
+			break;
+
 		default:
 			elog(ERROR, "unrecognized node type: %d", (int) nodeTag(node));
 			break;
@@ -328,6 +336,16 @@ ExecSupportsMarkRestore(NodeTag plantype)
 		case T_Sort:
 			return true;
 
+		case T_Result:
+			/*
+			 * T_Result only supports mark/restore if it has a child plan
+			 * that does, so we do not have enough information to give a
+			 * really correct answer.  However, for current uses it's
+			 * enough to always say "false", because this routine is not
+			 * asked about gating Result plans, only base-case Results.
+			 */
+			return false;
+
 		default:
 			break;
 	}