s3:smbd: fix posix acls when setting an ACL without explicit ACE for the owner (bug...

s3:smbd: fix posix acls when setting an ACL without explicit ACE for the owner (bug#2346)

The problem of bug #2346 remains for users exported by
winbindd, because create_token_from_username() just fakes
the token when the user is not in the local sam domain. This causes
user_in_group_sid() to give totally wrong results.
In uid_entry_in_group() we need to check if we already
have the full unix token in the current_user struct.
If so we should use the current_user unix token,
instead of doing a very complex user_in_group_sid()
which doesn't give reliable results anyway.

metze
(cherry picked from commit b79eff843be392f3065e912edca1434081d93c44)