to check for it and always returned 'true' for vtkobjects.

     Virtual methods are not hooked through from C++ to Python.
     So far only a limited set of special methods are supported:
     __init__ __getattr__ __setattr__ __delattr__ __call__ __str__ __repr__
     The isinstance(), issubclass() methods only work with vtk 2.1 and up.

new filter to mask fields/attributes.  flags can be set on individual fields or attributes in the input dataset and prevent the arrays from being copied to the output

ERR: Fixed library dependency problem on OSX python build