[Dovecot] File synchronization friendly indexes

[Aredridel]

I've been doing some tests of file synchronization with Unison (think
"two way rsync"), and run into one problem: Synching between servers has
conflicts on the index file.  I can manually exclude, but what seems to
me to be a really wonderful feature would be to, preferably, make the
indexes somewhat atomic, so that files, once written, don't change (this
is a feature of maildirs in general), and barring that, that they
include the machine name as part of the filename, so there's no
conflicts.

Also, on a completely unrelated and somewhat offtopic note: I'd love to
hear some brainstorms on how to prevent duplicate messages when maildirs
are synched, files are moved from new on one or more ends, flags are
changed inconsistently, and synched back.

Ari