The listener interface for receiving temp unit events. A class interested in temp unit events
implements this interface and registers with an instance of the EventDispatcher class to receive
such events. Temp unit events are issued when a temporary unit is created or deleted.
Invoked when a temporary unit is deleted. Beware! It is not clear if the temp unit has already
been deleted from the GameData or not. You should not assume that it is in a sane state. This
might be a FIXME.