Fixes several smaller bugs. Finally works with FreeBSD (tested with 4.7 and 5.0). I think there's still some problems with authentication failing sometimes due to memory/ipc corruption. I haven't seen those today, but I don't think I've fixed that either..

One behaviour change is that if default_mail_env isn't set and mbox format is detected (~/mail dir), /var/mail/user or /var/spool/mail/user is used as INBOX if found.