* The Problem:

  TNT does not properly support multiple heads.

  The problems include:

	1. References to framebuffer
	   Need to change uses of "framebuffer" to whichever is most
	   appropriate:
		framebuffer		default framebuffer defined in userdict
					screen specified in $DISPLAY
		framebufferof		framebuffer of the object in question
		currentframebuffer	framebuffer under the cursor
		globalroot		global coordinates
	2. Shared menus
	   Need to key shared menus off of "framebufferof".
	   Factor out shared menu creation code to procedures that take
	   framebuffer as argument and return menu. 
	   named /<title>Menu that makes entire menu tree and replaces itself
	   in class with shared class menu.
	   
	   Promote /Menu instance variable the first time it's used (/setmenu).
	   Factor out menu initialization in ClassDrawable to MenuInit.
	3. Window placement
	   Need to key placement information off of "framebufferof" or window parent.
	4. World crossing notification
	   Track service notification if client asks for it in /TrackStart.
	   Selection service drag notification.
	5. Selecting a default display
	   Need -display host:server.screen argument to pass down screen and set
	   up framebuffer in userdict.
	6. Default service
	   Listen for properties on framebuffer 0.
	   There may be some properties that are framebuffer specific.