(get_supplementary_group_sidlist): Evolve into get_unix_group_sidlist.
(get_user_local_groups): Add check for duplicates.
(get_user_primary_group): Suppress.
(get_group_sidlist): Silently ignore PDC unavailability.
Call get_unix_group_sidlist() before get_user_local_groups().
Remove call to get_supplementary_group_sidlist(). Never call
get_user_primary_group() as the passwd group is always included.
Add well_known_authenticated_users_sid in only one statement.