QPIDJMS-3: some minor cleanup and rationalisation, replace PHTODO with
TODO in comments to leverage standard IDE etc matching rules, use 'Not
Implemented' in exception message to avoid duplicate TODO pickup by tools.

git-svn-id: https://svn.apache.org/repos/asf/qpid/jms/trunk@1529205 13f79535-47bb-0310-9956-ffa450edef68