consider that SUGROUP and ROOTAUTH group contain the names of
users and groups. If user is not found in the list check_ingroup()
recurses on each member until either user is found or end of chain
is reached.
The above allows su's use of the wheel group to be extended to a large
number of users without necessarily putting them in group wheel, and
in a way that will work over NIS that simply extending the line length
limit in getgrent.c cannot.