Fix running through all tst_qqmlecmascript tests

* Implement SetHiddenField/GetHiddenField (hack)
* Fix recursive calls to SetEngine, to allow for the re-use of
  the QQmlEngine member in tst_qqmlecmascript after ~QQmlEngine
  was called on another instance
* Fix array sizing in function call parameter handling
* Don't try to clone the function object in Qt.binding (assert instead)

Change-Id: Ia3155dea8518348ec329037ca04e5c38e47a4f92
Reviewed-by: Lars Knoll <lars.knoll@digia.com>