OF-588: Making more of pubsub Serializable. As with the previous commit, I'm not to sure this is the right way to go, but I'd like to see if this provides a band-aid for the issue.

git-svn-id: http://svn.igniterealtime.org/svn/repos/openfire/trunk@13352 b35dd754-fafc-0310-a699-88a17e54d16e