Use PyObject_GetAttrWrapper in Pyston instead access PyClassObject directly.

The PyClassObject is an opaque pointer in Pyston. Don't access its member
directly. Use PyObject_GetAttrWrapper instead.

src/zope/proxy/_zope_proxy_proxy.c

@@ -173,6 +173,7 @@ WrapperType_Lookup(PyTypeObject *type, PyObject *name)
         base = PyTuple_GET_ITEM(mro, i);
 
         if (((PyTypeObject *)base) != &ProxyType) {
+/*
             if (PyClass_Check(base))
                 dict = ((PyClassObject *)base)->cl_dict;
             else {
@@ -180,6 +181,8 @@ WrapperType_Lookup(PyTypeObject *type, PyObject *name)
                 dict = ((PyTypeObject *)base)->tp_dict;
             }
             assert(dict && PyDict_Check(dict));
+*/
+            dict = PyObject_GetAttrWrapper(base);
             res = PyDict_GetItem(dict, name);
             if (res != NULL)
                 return res;