- 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

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)

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

Don't bother passing a freshly-zeroed mbstate to mbsrtowcs() etc.
when the current implementation won't use it, anyway. Just pass NULL.
This will need to be changed when state-dependent encodings are
supported, but there's no need to take the performance hit
in the meantime.

MFp4: Implementations of the wcstof() and wcstold() functions.