- Copy stable/10 (r259064) to releng/10.0 as part of the
10.0-RELEASE cycle.
- Update __FreeBSD_version [1]
- Set branch name to -RC1

[1] 10.0-CURRENT __FreeBSD_version value ended at '55', so
start releng/10.0 at '100' so the branch is started with
a value ending in zero.

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

Add <uchar.h>.

The <uchar.h> header, part of C11, adds a small number of utility
functions for 16/32-bit "universal" characters, which may or may not be
UTF-16/32. As our wchar_t is already ISO 10646, simply add light-weight
wrappers around wcrtomb() and mbrtowc().

While there, also add (non-yet-standard) _l functions, similar to the
ones we already have for the other locale-dependent functions.

Reviewed by: theraven

Remove regression tests for the obsolete rune interface.

Add test programs for mbsnrtowcs() and wcsnrtombs().

Add regression tests for sgetrune() and sputrune().

Regression tests for wctype(), iswctype(), wctrans(), towctrans().

Add regression tests for mblen(), mbtowc(), wctomb(), mbstowcs() and
wcstombs(). These tests have already found two libc bugs.

Simplify by using inference rules properly.

Add tests for btowc(), mbrlen(), mbsrtowcs() and wcsrtombs().

Add regression tests for mbrtowc(3) and wcrtomb(3).