An interface for a message filter. A message filter allows selection
of a subset of messages from a set of messages. Message filters are
typically used to select messages meeting a certain criteria from the
incoming message queue.
Returns true if a message matches the criteria, false otherwise. An
implementing class must override this method to provide the appropriate
selection criteria for the message filter.
Parameters:
m - message to check.
Returns:
true if the message matches the criteria, false otherwise.