Multiple inheritance causes a MRO error

[flosch]

Following piece of code causes the following MRO error:

class A(Document): pass
class B(A): pass
class C(B): pass

The relevant python traceback:

...
  File "/Users/flosch/devlibs/3rdparty/mongoengine/base.py", line 235, in __new__
    new_class = super_new(cls, name, bases, attrs)
  File "/Users/flosch/devlibs/3rdparty/mongoengine/base.py", line 177, in __new__
    or (DoesNotExist,), module))
  File "/Users/flosch/devlibs/3rdparty/mongoengine/base.py", line 444, in subclass_exception
    return type(name, parents, {'__module__': module})
TypeError: Error when calling the metaclass bases
    Cannot create a consistent method resolution
order (MRO) for bases DoesNotExist, DoesNotExist

(using: mongoengine master, pymongo 1.6, python 2.6.5, Mac OS X Snow Leopard)

[flosch]

Duplicate of http://github.com/hmarr/mongoengine/issues#issue/39