objtype: Fix passing of class param to inherited classmethods.

This is getting more and more tangled, but that's old news.

tests/basics/subclass_classmethod.py

@@ -0,0 +1,12 @@
+# Calling an inherited classmethod
+class Base:
+
+    @classmethod
+    def foo(cls):
+        print(cls.__name__)
+
+class Sub(Base):
+    pass
+
+
+Sub.foo()