[Samba] Make Winbind/PAM not return domain part for usernames

[George]

Ok, I figured out a way to make all this work in my case. I made Exim use
Dovecot LDA transport instead of "local delivery". With dovecot_delivery
transport you can specify "-d username" (would be "-d $local_part" in case
of Exim), which will trigger the same userdb lookup that Dovecot will do
later to fetch the mails from the files. So now the mails are delivered by
Exim and fetched by Dovecot from the same location, when using AD users.
Hope this helps somebody else.

Anyway, the issue with the "winbind use default domain" option not working
will need to be resolved at some point.

Best regards!