[Dovecot] dspam plugin

[Johannes Berg]

The first version is available at 
http://johannes.sipsolutions.net/edit/Projects/dovecot-dspam-integration/code

I'm calling dspam for every message, that seemed easier for now. I will 
probably integrate Tom's idea about storing the messages until a 
cron-job picks them up at night by just storing signatures into mysql, 
in which case its easy to do with a single query:

INSERT INTO new_spam (user, signature, isspam)
  VALUES (<user>, <signature>, <isspam>)
  ON DUPLICATE KEY UPDATE isspam = <isspam>

with given values for <user>, <signature> and <isspam> and a key on 
(user, signature).

For now, however, calling dspam for every message works good enough for 
me, and seems to work.

Regards,
Johannes