[imp] Message threading

[Rudi Benkovič]

> Yes, and php has an imap_thread() call now. All of the pieces are there -
> except someone to put them together. :)  It's definitely on my
> "should do this
> since it's cool and useful" list, but it won't make it to the top of my list
> anytime soon...

I have already done this for my webmail <http://jawmail.sourceforge.net/>. You
can use the list-thread class from it for IMP. It's pre-alpha non-documented
only-in-the-changelog-feature, but it is, and it works :)