Fix super call goto for multiple inheritance, fixes #1311

jedi/evaluate/base_context.py

@@ -241,7 +241,7 @@ class _ContextWrapperBase(HelperContextMixin):
         return cls(*args, **kwargs)
 
     def __getattr__(self, name):
-        assert name != '_wrapped_context'
+        assert name != '_wrapped_context', 'Problem with _get_wrapped_context'
         return getattr(self._wrapped_context, name)