Patch for Issue #3 + Resolution of Issue #4.

This commit approves that with the help of InterceptorWrapper (global interceptor) BeanTesting already supports correct transaction propagation in EJB interceptors. The transaction will be shared among invoked interceptor instances.

Details:

* The patch for Issue #3 includes a modification of InterceptorWrapperImpl. During the verification of the proposed bug by @agori (see issue  #4), I observed in TestEJBInterceptedByMultipleInterceptors a ClassCastException: occurs if an intercepted @EJB returns a value in a business method. The reason behind it was that InterceptorWrapperImpl didn´t returned results from invoked interceptor instances but rather the origin InvocationContext.
* Resolution of Issue #4: the created test case (TestEJBInterceptedByMultipleInterceptors) demonstrates that EJB interceptors (Interceptor1SharingTransaction and Interceptor2SharingTransaction) are using the same (active) transaction.