addition test for JAXBcontext when callback is used but only reference to Endpoint reference is nested in a complex type

This test validates the jaxb context can pick up endpoint reference types and hence ws addressing dependencies even when the endpoint reference type is used for a call-back and the type is nested in a complex type. This is a variation of the basic_callback_test that once showed up an error but was not merged at that time.
It would be no harm to include it to ensure we don't ever regress.