Message handlers don't track MessageID for dupes

A problem has surfaced in the handling of incoming messages for use with FullComment/NonQuoted message handlers etc.

The problem is that JIRA is not tracking the Message-ID's when it creates the comment inside JIRA for already being processed.

This triggers the comment being processed multiple times. Normally this isn't a problem with POP3 as the messages would be deleted from the server as their read, but in the case of my NNTP polling service, if the same message is read for any reason, it triggers a new comment....