Update to Dovecot 1.1.18.

+ dovecot -n/-a now outputs also lda settings.
- Maildir++ quota: Quota was sometimes updated wrong when it was
  being recalculated.
- Searching quoted-printable message body internally converted "_"
  characters to spaces and didn't match search keys with "_".
- Messages in year's first/last day may have had broken timezones
  with OSes not having struct tm->tm_gmtoff (e.g. Solaris).

(ghen)