probes and use of isMemberOf vs isKindOf

[Marcus G. Daniels]

In src/simtools/{ClassDisplayWidget,ObjectSaver,SimpleProbeDisplay}.m,
and src/swarmobject/ProbeMap.m, there are conditionals like 

   if([probe isMemberOf: [VarProbe class]]){ 

   if([probe isMemberOf: [MessageProbe class]]){ 

Why are these wired to these classes?  Why prohibit subclassing of
VarProbe and MessageProbe?

                  ==================================
   Swarm-Support is for discussion of the technical details of the day
   to day usage of Swarm.  For list administration needs (esp.
   [un]subscribing), please send a message to <address@hidden>
   with "help" in the body of the message.
                  ==================================