DynamicMenuUpdates

Here is an example of how to update the label, checked and enabled state of a menu item:

	item := menu addItem: 'a menu item'.
	item updateLabel:['label: ', label] 
		when:{self. #labelChanged}.
	item updateChecked:[foo = true] 
		when:{self. #fooChanged}.
	item updateEnabled:[foo ~= nil] 
		when:{self. #fooChanged}.