Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Implement rpmatch(), a semi-standard interface (as found on AIX, Tru64,
GNU) for determining whether a string is an affirmative or negative
response to a question according to the current locale. This is done
by matching the response against nl_langinfo(3) items YESEXPR and NOEXPR.