[Dovecot] [patch] support tpop3d-style UIDLs

Hello,

I've attached a patch that adds an additional expando to pop3_uidl_format. The additional expando (%M) expands to the md5sum of the filename (which is already available via %f.) This UIDL style is compatible with tpop3d when using Maildir.

The patch is against dovecot 1.0 beta3, and I'd love to see it be merged into the official tree. Comments welcome.

-- Ben Winslow <rain@bluecherry.net>