v2.2.21 released

[Timo Sirainen]

http://dovecot.org/releases/2.2/dovecot-2.2.21.tar.gz
http://dovecot.org/releases/2.2/dovecot-2.2.21.tar.gz.sig

Due to a bit bad doveadm bugs in v2.2.20 here's a fixed v2.2.21. Also from this release forward we're finally using git with branches to make new releases. So new releases will have a bit more time to stabilize in the branch before they're being released (while still allowing new features to be developed in the master development branch). We already did something like this for the enterprise releases, but now it's done for community releases as well.

 - doveadm mailbox list (and some others) were broken in v2.2.20
 - director: Fixed making backend changes when running with only a
   single director server.
 - virtual plugin: Fixed crash when trying to open nonexistent
   autocreated backend mailbox.