Log Message:
Update to Dovecot 2.1.6

* Session ID is now included by default in auth and login process log lines. It
  can be added to mail processes also by adding %{session} to mail_log_prefix.
+ Added ssl_require_crl setting, which specifies if CRL check must be successful
  when verifying client certificates.
+ Added mail_shared_explicit_inbox setting to specify if a shared INBOX should
  be accessible as "shared/$user" or "shared/$user/INBOX".
- v2.1.5: Using "~/" as mail_location or elsewhere failed to actually \ 
expand it
  to home directory.
- dbox: Fixed potential assert-crash when reading dbox files.
- trash plugin: Fixed behavior when quota is already over limit.
- mail_log plugin: Logging "copy" event didn't work.
- Proxying to backend server with SSL: Verifying server certificate name always
  failed, because it was compared to an IP address.