Give correct error message when Object.isExtensible is called on a non object (fixes issue 1452)

src/v8natives.js

Index: src/v8natives.js
===================================================================
--- src/v8natives.js	(revision 8272)
+++ src/v8natives.js	(working copy)
@@ -1016,7 +1016,7 @@
 // ES5 section 15.2.3.13
 function ObjectIsExtensible(obj) {
   if (!IS_SPEC_OBJECT(obj)) {
-    throw MakeTypeError("obj_ctor_property_non_object", ["preventExtension"]);
+    throw MakeTypeError("obj_ctor_property_non_object", ["isExtensible"]);
   }
   return %IsExtensible(obj);
 }