touch duplicate group suppression, but the merge blew away our
duplicate group suppression.
The merge also blew away the -Wall cleanup in rev.1.5, but that
was misformatted, so I didn't restore it.
in an (unlikely) border case (maxgroups==1 and the user is on
an /etc/group line for the same group and that group only ...).
Now this case is dealt with as before ...