Moving messages redux

[Edward Z. Yang]

Excerpts from Sebastian Spaeth's message of Fri Aug 31 19:44:35 -0400 2012:
> Hey, that sounds cool! It would be nice to be cleverer about moves
> between folders. On the downside, offlineimap would have to run and
> listen while you move files. (and usually other MUAs would move from
> folderA/cur to folderB/tmp to folderB/cur, or would they move directly?)

If we have some assistance from the mail client, we don't need inotify.
I made up a tiny little extension to Maildir, which adds a 'mv' folder
which contains the name of the file (now missing), and the full path
to the new location it was moved to, and taught Sup and OfflineIMAP
how to read the format.  So the mail client writes a log of moves, and
OfflineIMAP reads out that log.  If the log is lost, no worries, we
just take the slow path.

Cheers,
Edward