debugger highlighting objects up the stack

Just a brief throw away idea to share before it floats off on its own,
it could be useful from the debugger being able to select a variable,
and for the object it contains, ask the debugger to highlight up the stack
where that object exists in variables and in code.
Could be complicated - may need to:
* autoscroll the debugger's inspector pane
* annotate previously sent messages with the identity hash of the
object returned

cheers -ben