Cann't inherit from singleton
Raise a TypeError when superclasses mismatch
Make RPython happy
Make RPython happy
Merge pull request #693 from krekoten/language_class

Class definition
Module#extend_object

Specs fixed:

Module#extend_object
- is called when #extend is called on an object
- extends the given object with its constants and methods by default
- is called even when private
Merge pull request #694 from krekoten/module_extend_object

Module#extend_object