This is the function that is called if there is no
filterState() method for a particular state name.
This default filter function behaves in one of two modes:
(1) if self.defaultTransitions is None, allow any request
whose name begins with a capital letter, which is assumed to
be a direct request to a particular state. This is similar to
the old ClassicFSM onUndefTransition=ALLOW, with no explicit
state transitions listed.
(2) if self.defaultTransitions is not None, allow only those
requests explicitly identified in this map. This is similar
to the old ClassicFSM onUndefTransition=DISALLOW, with an
explicit list of allowed state transitions.
Specialized FSM's may wish to redefine this default filter
(for instance, to always return the request itself, thus
allowing any transition.).