Fix deprecated python type check in TestSubClass.

Now that the python wrappers use type objects for VTK classes, calling
type(obj) returns the class type, rather than 'vtkobject'.

Common/Core/Testing/Python/TestSubClass.py

@@ -34,7 +34,7 @@ class vtkCustomObject(vtk.vtkObject):
     def SetExtraObject(self, o):
         """Setter method."""
         # make sure it is "None" or a vtkobject instance
-        if o == None or type(o) == type(self):
+        if o == None or isinstance(o, vtk.vtkObjectBase):
             self._ExtraObject = o
             self.Modified()
         else: