DBMail progress

This week I got a bunch of DBMail stuff done:

• Loadable database modules. Then Paul reorganized the files into a single, consistent dbmail/modules directory, and that inspired me to to authentication and sort modularization. Still a few tweaks left to do on auth, and the guts of sort are totally not figured out yet.
• Cleared the way for Sieve reintegration, handling username+mailbox@domain addressing, and better stderr debugging.
• Lots of updates on the DBMail Wiki so that people can find out what’s cooking.