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)

Introduce new encoding: "ASCII"
It differs from default C/POSIX "NONE" mainly by stricter 8bit check
for mb*towc*/wc*tomb* family, returning EILSEQ

- Include runetype.h for _RuneLocale_

. Static'ize functions exported via function reference variables only.
. Replace inclusion of sys/param.h to sys/cdefs.h and sys/types.h where
appropriate.
. move _*_init() prototypes to mblocal.h, and remove these prototypes
from .c files
. use _none_init() in __setrunelocale() instead of duplicating code
. move __mb* variables from table.c to none.c allowing us to not to
export _none_*() externs, and appropriately remove them from mblocal.h

Ok'ed by: tjr

Remove the obsolete <rune.h> interface.

Implement the GNU extensions of mbsnrtowcs() and wcsnrtombs(). These are
convenient when the source string isn't null-terminated.

Implement the other conversion functions (mbstowcs(), mbsrtowcs(), wcstombs(),
wcsrtombs()) in terms of these new functions.

Allow encoding modules to override the default implementations of
mbsrtowcs() and wcsrtombs(). Provide a fast implementation for the
trivial "NONE" encoding.

Move prototypes of various encoding-related functions into a new header
file to avoid extern'ing them all over the place.