In zope ExtensionClass, it just copied and inlined the codes from CPython's
PyObject_GenericGetAttr and _PyObject_GetDictPtr. Which are not work for Pyston.
So just call correspond function in Pyston.

In Pyston, PyClassObject is just an opaque pointer. Don't access it directly.
Use PyObject_GetAttrWrapper which provided by Pyston:

-        d = ((PyClassObject *)cls)->cl_dict;
+        d = PyObject_GetAttrWrapper(cls);