[Dovecot] Suggestion: deliver should honor mail_log_prefix

[Mike Abbott]

I can set the log prefix for imap/pop3 processes using mail_log_prefix  
but the log prefix for deliver is hard-coded.  (I'm using 1.1.13.)   
Deliver should either honor mail_log_prefix or have its own setting  
(deliver_log_prefix?).  What do you think?