r22710: Support one-way trusts.
* Rely on the fact that name2sid will work for any name
in a trusted domain will work against our primary domain
(even in the absense of an incoming trust path)
* Only logons will reliably work and the idmap backend
is responsible for being able to manage id's without contacting
the trusted domain
* "getent passwd" and "getent group" for trusted users and groups
will work but we cannot get the group membership of a user in any
fashion without the user first logging on (via NTLM or krb5)
and the netsamlogon_cache being updated.
(This used to be commit
dee2bce2af6aab8308dcef4109cc5248cfba5ef5)