This is an abstract superclass for models which want to use the #when:send:to: event system in an efficient way. Instances of this class keep their own list of event symbols and registered events instead of using the global class variable EventsFields in class Object.

Structure:
myEvents Dictionary -- set of event symbols and registered listeners

	events	top
	myEvents Private. Answer a Dictionary with the receiver's events or nil if no events have been registered. Subclasses may overwrite this method for performance reasons.
	myEvents: Private. Set (or remove) the receiver's dictionary of events. Subclasses may overwrite this method for performance reasons.