We currently use strings as header names. Since a header has to have a magic number, we can replace strings with shorts. A short is always 2 bytes and we don't need to send (potentially long) names around.

A message would then have a Headers hashmap of shorts and Headers. A protocol would also have to be able to catch its own headers, e.g. by creating a method getId(). UDP.getId() might return 56, which is the value in jg-magic-map.xml for TpHeader.

This will solve https://jira.jboss.org/jira/browse/JGRP-872.