has() returns true for internal dependencies.

[shochdoerfer]

AnnotationBeanFactory::has() returns true for "internal dependencies" (methods in config class marked as protected) since method_exists() simply checks if the method does exists not if the method can actually be called from the current context. This is a problem when AnnotationBeanFactory::get() is called since call_user_func() is not able to call the method as intended.

To fix the problem substitute the method_exists() call with is_callable(). This seems to be a side-effect of #10.

[shochdoerfer]

Fixed with #39.