code: def fstyle_changed(self, settings, key, user_data):
          
          font = Pango.FontDescription(settings.get_string(key))
          for i in self.guake.notebook_manager.iter_terminals():
              i.set_font(font)
docs: If the gconf var style/font/style be changed, this method
          will be called and will change the font style in all terminals
          open.