Added support for a custom SASL mechanism called 'CLEARSPACE' for use with Clearspace's group chat authentication. This is handled by a new SaslServer called ClearspaceSaslServer.

git-svn-id: http://svn.igniterealtime.org/svn/repos/openfire/trunk@9957 b35dd754-fafc-0310-a699-88a17e54d16e