fixing button theming with GtkBuilder

This is a bit icky. It would be neater if the Python bindings exposed hildon_gtk_widget_set_theme_size(), but not much. So, to fix the button theming if you've created your interface with GtkBuilder, it looks something like this:

# these aren't exported anywhere, copied from Maemo GTK+
HILDON_HEIGHT_FINGER = 70
HILDON_HEIGHT_THUMB = 105

# fix theming
for widget in self.ui.get_objects():
    if not isinstance(widget, gtk.Button): continue
    # hildon_gtk_widget_set_theme_size is not bound into Python
    if widget.get_name().startswith('largebutton'):
        widget.set_size_request(-1, HILDON_HEIGHT_THUMB)
    elif widget.get_name().startswith('kpbutton'):
        widget.set_size_request(HILDON_HEIGHT_THUMB, HILDON_HEIGHT_THUMB)
    widget.set_name('HildonButton-thumb')