- Fix typos in comments in hash.c.
- Remove unneeded and unused member from grouplist struct in hash.h.
(Curiously, the compiler never complained about this even though the
member was of type 'struct grps' which is not defined anywhere in
this program.)
- char ch -> int ch in revnetgroup.c.
- char *argv[0]; -> char *argv[]; also in revnetgroup.c.
- Force the user to specify at least one of the -u or -h flags
and complain if they specify both.
