Implement objectiterator on top of an iterator method in the vtbl

This makes it easier to implement the array-like wrapper classes
for qml lists and qt lists.

Change-Id: I169025a3e9c76951c0778bcda4bbb1f9a8afc8a0
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Regression: Fix various failures in test262

The stack property added to Error objects must not be enumerable.

Change-Id: Ie163cff2d9c41997e95afa6dd32275be6b4b310d
Reviewed-by: Lars Knoll <lars.knoll@digia.com>