This patch adds a new class, ToggleItem, to ROX-Lib2's
Menu.py. This class can be used in the Action-based
menu system to support Toggle (check) menu items. The
class provides an initial 'state' parameter to set the
starting state of the item. It also stores the
gtk.CheckMenuItem widget in its .widget memer so that
the value of the menu can be toggled under application
control. This patch is against ROX-Lib2 1.9.13.