Log Message:
v0.4.16:
* Part of the Sieve extprograms implementation was moved to Dovecot, which
  means that this release depends on Dovecot v2.2.26+.
* ManageSieve: The PUTSCRIPT command now allows uploading empty Sieve scripts.
  There was really no good reason to disallow doing that.
+ Sieve vnd.dovecot.report extension:
  + Added a Dovecot-Reporting-User field to the report body, which contains
    the e-mail address of the user sending the report.
  + Added support for configuring the "From:" address used in the report.
+ LDA sieve plugin: Implemented support for a "discard script" that is run
  when the message is going to be discarded. This allows doing something other
  than throwing the message away for good.
+ Sieve vnd.dovecot.environment extension: Added vnd.dovecot.config.*
  environment items. These environment items map to sieve_env_* settings from
  the plugin {} section in the configuration. Such values can of course also
  be returned from userdb.
+ Sieve vacation extension: Use the Microsoft X-Auto-Response-Suppress header
  to prevent unwanted responses from and to (older) Microsoft products.
+ ManageSieve: Added rawlog_dir setting to store ManageSieve traffic logs.
  This replaces at least partially the rawlog plugin (mimics similar IMAP/POP3
  change).
- doveadm sieve plugin: synchronization: Prevent setting file timestamps to
  unix epoch time. This occurred when Dovecot passed the timestamp as
  'unknown' during synchronization.
- Sieve exprograms plugin: Fixed spurious '+' sometimes returned at the end
  of socket-based program output.
- imapsieve plugin: Fixed crash occurring in specific situations.
- Performed various fixes based on static analysis and Clang warnings.