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

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

Add category definitions (which were missing) for locale categories LC_MESSAGES,
LC_NUMERIC, LC_MONETARY. Information source is POSIX locale defintions
collection at ftp://dkuug.dk/i18n/WG15-collection/