Fix wording: secondary -> subordinate.

	* libmisc/find_new_sub_gids.c: Fix wording: secondary ->
	subordinate.
	* libmisc/find_new_sub_uids.c: Likewise.
Editorial changes to usermod(8)

	* man/usermod.8.xml: Fix typos and wording.
	* man/usermod.8.xml: Add references to subgid(5) and subuid(5).
check for ruserok existence

rlogin support is old school code, so newer C libraries drop support for
ruserok (like uClibc, optionally).  But shadow doesn't build with that,
so have it check for ruserok to optionally enable rlogin.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Fix for Alioth#314271 (musl libc)

	* libmisc/utmp.c: Add include files needed for getaddrinfo().
	See Alioth#314271