dovecot2: updated to 2.3.4

2.3.4:
* The default postmaster_address is now "postmaster@<user domain or
  server hostname>". If username contains the @domain part, that's
  used. If not, then the server's hostname is used.
* "doveadm stats dump" now returns two decimals for the "avg" field.

+ Added push notification driver that uses a Lua script
+ Added new SQL, DNS and connection events.
  See https://wiki2.dovecot.org/Events
+ Added "doveadm mailbox cache purge" command.
+ Added events API support for Lua scripts
+ doveadm force-resync -f parameter performs "index fsck" while opening
  the index. This may be useful to fix some types of broken index files.
  This may become the default behavior in a later version.
- director: Kicking a user crashes if login process is very slow
- pop3_no_flag_updates=no: Don't expunge DELEted and RETRed messages
  unless QUIT is sent.
- auth: Fix crypt() segfault with glibc-2.28+
- imap: Running UID FILTER script with errors assert-crashes
- dsync, pop3-migration: POP3 UIDLs weren't added to
  dovecot.index.cache while mails were saved.
- dict clients may have been using 100% CPU while waiting for dict
  server to finish commands.
- doveadm user: Fixed user listing via HTTP API
- All levels of Cassandra log messages were logged as Dovecot errors.
- http/smtp client may have crashed after SSL handshake
- Lua auth converted strings that looked like numbers into numbers.

(adam)