[pygtk] Switching pixmaps using GtkPixmap.set()

[Tessa Lau]

> Use "pix2, mask = img2.get_pixmap()" here instead of
> make_pixmap().  Make_pixmap returns a new GtkPixmap widget rather than a
> GdkPixmap/GdkBitmap pair.

That's closer... but that gives me this error:
TypeError: gtk_pixmap_set, argument 3: expected GdkWindow, None found

The mask returned by get_pixmap() is None.  Is that supposed to happen?

--Tessa