Group termination updates

Title: Group termination updates

Here is a consolidation of all points discussed about group termination, persistence/timeout parameters.

I think it addresses every point we got feedback on.

It results in a cleaner, more concise Section 5 that I drafted, attached.

Termination rules are simpler (athough as many as before, but no subcases anymore...), 

and do not need to refer to such concrete notion as  "group state".

For review.

Jacques

 <<Group-Termination.sxw>> 

Group-Termination.sxw