Added the kerberos 5 implementation the Martin Swales has contributed.

There was some changes to the original implementation that include the
renaming of the package of the added classes, replacement of the non-standard
base64 classes with standard versions and replacing the logging
mechanism with the jgroups specific version.
Merge branch 'master' of https://github.com/ccorsi/JGroups into JGRP-1657
First commit of Kerberos based authentication. Originally written by Martin Swales, added by Claudio Corsi (https://issues.jboss.org/browse/JGRP-1657)