- Copy stable/10@296371 to releng/10.3 in preparation for 10.3-RC1
builds.
- Update newvers.sh to reflect RC1.
- Update __FreeBSD_version to reflect 10.3.
- Update default pkg(8) configuration to use the quarterly branch.

Approved by: re (implicit)

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)

Remove unnecessary #include directives.

Remove useless checks for characters longer than INT_MAX bytes.

Reduce overhead by calling internal versions of the multibyte conversion
functions directly wherever possible.

Prepare to handle state-dependent encodings. This mainly involves not
taking shortcuts when it comes to storing and passing around conversion
states.

Implement mbtowc() in terms of mbrtowc(), and wctomb() in terms of wcrtomb().

Handle boundary cases more correctly; mblen(s, 0) and mbtowc(NULL, s, 0)
return -1 regardless of what s points to, mbtowc(&w, s, 1) sets w to a
null wide character when s points to a null byte. This seems to be closer
to what most other implementations do, but the C99 standard contradicts
itself for these cases.

Style sweep.

Style: One space between "restrict" qualifier and "*".

Set errno to EILSEQ when invalid multibyte sequences are detected
(XSI extension to 1003.1-2001).

Add restrict qualifiers to the arguments of mbstowcs, mbtowc() and
wcstombs().

Split ansi.c into a separate source file for each function.