[gef-dev] changes to add/removeNotify in Figure

[Randy Hudson <hudsonr@xxxxxxxxxx>]

(Most GEF users should not have to worry
about this change.  add/removeNotify is used by connections to hookup
anchor listeners, and in a few other places.)

The Figure implementation now checks
to prevent addNotify from being called 2 or more times successively.  Previously,
addNotify() would be called if you added a figure to another figure.  Then,
it would be called *again* if you added that parent figure to something
else, etc.  This case is pretty rare but could cause listener leaks
to occur.

The new behavior is:
- When adding, addNotify() is only called
on a figure if it has been called on it's parent too.  Otherwise,
it will be called later when/if the parent's addNotify() happens.
- Same behavior as before, except removeNotify()
is only called on a figure if addNotify() was last called.  Also,
removeNotify() will not be called more than once in succession.
- Any root figure needs to have addNotify()
called on it to bootstrap the process.  LightweightSystem does this
now.

This is nothing to get excited about.
 The purpose of this change is to make the method do what you thought
it was already doing.

-Randy