[Dovecot] v2.2: Fix to slow process creation in some setups

Especially some imap/pop3 login bursts could have caused errors like:

imap-login: Error: net_connect_unix(imap) failed: Resource temporarily unavailable

Fix in http://hg.dovecot.org/dovecot-2.2/rev/69179ca6007d

Explanation & workaround in http://wiki2.dovecot.org/SocketUnavailable :

Dovecot v2.2.0 - v2.2.6 were attempting to optimize host.domain lookups by doing them only once in the master process. Unfortunately they were actually doing the lookup every time when creating a new process. In some configuration this lookup could have done a somewhat slow DNS lookup, causing the process creation to become very slow and triggering this message.

The fix is in v2.2.7 and you can also workaround this:

• Add to dovecof.conf: import_environment = TZ DEBUG_OUTOFMEM DOVECOT_HOSTDOMAIN
• Before "dovecot" binary is started, run: export DOVECOT_HOSTDOMAIN=mailserver.example.com (of course changing the value)