Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

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

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

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

Implement xlocale APIs from Darwin, mainly for use by libc++. This adds a
load of _l suffixed versions of various standard library functions that use
the global locale, making them take an explicit locale parameter. Also
adds support for per-thread locales. This work was funded by the FreeBSD
Foundation.

Please test any code you have that uses the C standard locale functions!

Reviewed by: das (gdtoa changes)
Approved by: dim (mentor)

Per Regents of the University of Calfornia letter, remove advertising
clause.

# If I've done so improperly on a file, please let me know.

Implement wcwidth() as an inline function.

Grab all the information we need about a character with one call to
__maskrune() instead of one direct call and one through iswprint().

Use modern-style arguments declaration

Write null wide-character as L'\0' like in other places

According to SUSv2, always return 0 for null wide-character code

Move internal defines from ctype.h here

Move wcwidth() to separate file, it doesn't belong to iswctype.c at all