[Dovecot] Patch to deliver

Hi Timo!

I wrote a little patch to add the capability of the deliver to customize the "subject" of the rejection messages. Now is possibly to translate the body and subject!

In dovecot.conf:

rejection_reason_subject = Automatically rejected mail to %t rejection_reason = Your message to <%t> was automatically rejected:%n%r

Please, review the patch! :D