Proposed frysk.rt.Display

[Adam Jocksch <ajocksch@redhat.com>]

 From a discussion with Andrew:
 > What is needed here is a higher level abstraction, a frysk.rt.Display 
(I'm not using Watch as that implies hardware
 > WatchPoint) object, say, that worries about scope rules, and changing 
location, and being able to save/restore
 > itself.  The display object, when the program stops, would know to 
re-instantiate the underlying Variable (if still in
 > scope) when the process stops.

So, mulling it over it sounds like frysk.rt.Display needs to have the 
following
    - an isInScope() method or something akin to it in functionality
    - some reference to the Variable itself. I'm guess that something 
like private Variable myVar is probably not what's
      needed here; so should we be storing the variable's Location? or 
the higher level source#line#col?
    - all of the value-access functionality already implemented in 
Variable (or a way to get a Variable from a Display,
      then call get Int or whatever on it)

The second point is probably the trickiest one, and the point where I 
have the least idea of what would be sufficient/best.

Adam