Failing test to reproduce the error with reflection and core classes

As reported in [Symfony2 Google group](https://groups.google.com/forum/?hl=en#!topic/symfony2/PpxQjNcG8BA), we found an issue with the reflection: MethodReflection is unable to read the source for the compiled classes (eg SoapClient, DateTime, etc).

    1) ZendTest\Code\Reflection\MethodReflectionTest::testGetContentsWithCoreClass
    file(): Filename cannot be empty

    /Users/stefanosala/Sites/src/zf2/library/Zend/Code/Reflection/MethodReflection.php:123
    /Users/stefanosala/Sites/src/zf2/tests/ZendTest/Code/Reflection/MethodReflectionTest.php:65

I created a test to reproduce this issue, but unfortunately I'm not able to find a patch. If anyone has a hint, just add a comment and I'll try to work on it.