Add protection against "wrong" marking in debug builds

Add protection against "wrong" marking in debug builds

To protect against situations where we accidentally mark an object that belongs
to a different engine - there are many possible entry points - this patch adds
an assertion in debug builds for this situation. When it happens, it will point
more or less directly to the code that tries to push an object to the wrong JS
stack for marking. This helped in the investigation of QTBUG-44895

Change-Id: I311b9ff6d282d52e725044b03a62cd77085536be
Reviewed-by: Lars Knoll <lars.knoll@digia.com>