r22710: Support one-way trusts.

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.