Don't re-wrap PHP objects from V8 to V8Object

Currently if a PHP object is passed to V8 it gets wrapped to a V8 object, so far so good.

However if the JavaScript side passes this object back to another PHP function, then V8Js currently wrapps the V8 object again, so the called function sees a PHP object of type `V8Object`.  Instead I would expect the called function to see the original PHP object on which it is able to call methods on (which in turn are able to access private & protected properties).

See the newly added test case tests/object_passback.phpt for what I'm trying to do :-)

I had to adapt the object_method_call.phpt test case, since it currently `var_dump`s passed back objects and hence had `V8Object` written down ...