The comment class could be streamlined and standardized by making it
subclass (Tree, email.Message).  This should make the per-bug, mini
mailing list more expressive, and add support for fancy email
features.  On the other hand, it could make the Comment/xml interface,
HTML production, etc. more awkward.

Time for another look at Debian's tracker, or do they only allow
text/plain, single-part messages?