Fix thinko in my recent change to put an explicit argisrow field in NullTest:

when the planner splits apart a ROW(...) IS NULL test, the argisrow values
of the component tests have to be determined from the component field types,
not copied from the original NullTest (in which argisrow is surely true).

src/backend/optimizer/util/clauses.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.283 2010/01/02 16:57:48 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.284 2010/01/19 16:33:33 tgl Exp $
  *
  * HISTORY
  *	  AUTHOR			DATE			MAJOR EVENT
@@ -2826,15 +2826,17 @@ eval_const_expressions_mutator(Node *node,
 											 context);
 		if (arg && IsA(arg, RowExpr))
 		{
-			RowExpr    *rarg = (RowExpr *) arg;
-			List	   *newargs = NIL;
-			ListCell   *l;
-
 			/*
 			 * We break ROW(...) IS [NOT] NULL into separate tests on its
 			 * component fields.  This form is usually more efficient to
 			 * evaluate, as well as being more amenable to optimization.
 			 */
+			RowExpr    *rarg = (RowExpr *) arg;
+			List	   *newargs = NIL;
+			ListCell   *l;
+
+			Assert(ntest->argisrow);
+
 			foreach(l, rarg->args)
 			{
 				Node	   *relem = (Node *) lfirst(l);
@@ -2856,7 +2858,7 @@ eval_const_expressions_mutator(Node *node,
 				newntest = makeNode(NullTest);
 				newntest->arg = (Expr *) relem;
 				newntest->nulltesttype = ntest->nulltesttype;
-				newntest->argisrow = ntest->argisrow;
+				newntest->argisrow = type_is_rowtype(exprType(relem));
 				newargs = lappend(newargs, newntest);
 			}
 			/* If all the inputs were constants, result is TRUE */