src/newusers.c, src/chpasswd.c, src/groupmems.c, src/usermod.c,
src/chgpasswd.c, src/vipw.c, src/su.c, src/useradd.c,
src/groupmod.c, src/passwd.c, src/groupadd.c, src/chage.c,
src/faillog.c, src/chsh.c: If someone uses the -h/--help options,
the usage should not go to stderr nor should the utility exit with
non-zero status. All of the shadow utils do just this
unfortunately, so convert them over to sanity.
* man/groupmems.8.xml, man/gpasswd.1.xml: Added option -h/--help.