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

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

Renumber clauses to reduce diffs to other versions

NetBSD, OpenBSD, and Android's Bionic number the clauses 1 through 3,
so follow suit to make comparison easier.

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.

Whitespace/style tweaking of prev. commit.

Noted by: bde

POSIX says that 0[xX] prefix is _optional_ even in base 16 case, make it
really so.

"If the value of base is 16, the characters 0x or 0X may optionally
precede the sequence of letters and digits, following the sign if
present."

Found by: joerg

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

- Add the 'restrict' qualifier to the function prototypes and
definitions of the functions that convert strings to numbers
and are defined by IEEE Std 1003-1.2001.
- Use ANSI-C function definitions for all of the functions
mentioned above plus strtouq and strtoq.
- Update the prototypes in the manual pages.

Fix the style of the SCM ID's.
I believe have made all of libc .c's as consistent as possible.

Return 'c' back to signed due to potential comparison problems
Use simpler test for valid ranges

Submitted by: bde

Make it works for non ASCII compatible encodings too.
The only assumption left is that 'A'..'Z' 'a'..'z' both are contiguous

Back out national digits support, POSIX explicetely disallows it:

The definition of character class digit requires that only ten characters
-the ones defining digits- can be specified; alternate digits (for
example, Hindi or Kanji) cannot be specified here. However, the encoding
may vary if an implementation supports more than one encoding.

The definition of character class xdigit requires that the characters
included in character class digit are included here also and allows for
different symbols for the hexadecimal digits 10 through 15.

Don't ever assume that isdigit() is always subset of isxdigit()

Implement strtoimax() and strtoumax()