code: def trayicon_toggled(self, settings, key, user_data):
          
          if hasattr(self.guake.tray_icon, 'set_status'):
              self.guake.tray_icon.set_status(settings.get_boolean(key))
          else:
              self.guake.tray_icon.set_visible(settings.get_boolean(key))
docs: If the gconf var use_trayicon be changed, this method will
          be called and will show/hide the trayicon.