Log Message:
Update to Dovecot 2.1.9

* mail-log plugin: Log mailbox names with UTF-8 everywhere (instead of mUTF-7
  in some places and UTF-8 in other places)
* director: Changed director_username_hash setting's default from %u to %Lu (=
  lowercase usernames). This doesn't break any existing installations, but
  might fix some of them.

+ doveadm: Added "auth cache flush [<username>]" command.
+ Implemented dict passdb/userdb
+ Implemented Redis and memcached dict backends, which can be used as auth
  backends. Redis can also be used as dict-quota backend.
+ Added plugin { quota_ignore_save_errors=yes } setting to allow saving a mail
  when quota lookup fails with temporary failure.
- Full text search indexing might have failed for some messages, always causing
  indexer-worker process to run out of memory.
- fts-lucene: Fixed handling SEARCH HEADER FROM/TO/SUBJECT/CC/BCC when the
  header wasn't lowercased.
- fts-squat: Fixed crash when searching a virtual mailbox.
- pop3: Fixed assert crash when doing UIDL on empty mailbox on some setups.
- auth: GSSAPI RFC compliancy and error handling fixes.
- Various fixes related to handling shared namespaces