Allow vtk-python override to work with ABCs

The type check in the override() method was too strict, it was not
allowing the override to be derived from an abstract base class.

Wrapping/PythonCore/PyVTKObject.cxx

@@ -51,7 +51,7 @@ static PyObject* PyVTKClass_override(PyObject* cls, PyObject* type)
   PyTypeObject* typeobj = (PyTypeObject*)cls;
   std::string clsName = vtkPythonUtil::StripModuleFromType(typeobj);
 
-  if (Py_TYPE(type) == &PyType_Type)
+  if (PyObject_TypeCheck(type, &PyType_Type))
   {
     PyTypeObject* newtypeobj = (PyTypeObject*)type;
     if (PyType_IsSubtype(newtypeobj, typeobj))