a minimal change to get appliance mode to work with winbindd

a minimal change to get appliance mode to work with winbindd

we needed to accept usernames of the form DOMAIN/user, which means we
needed to pass the domain to a getpwnam() like routine in certain
critical spots.

What I'd rather do is get rid of "char *user" everywhere and use the
new userdom_struct, but that will have to wait a few days.
(This used to be commit 8b7a10febead8be182e7d5b1d68259e31530b69c)