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)

Per Regents of the University of Calfornia letter, remove advertising
clause.

# If I've done so improperly on a file, please let me know.

Include a couple of headers to ensure consistency between the prototype and
the function definition.

Prefer <runetype.h> to <rune.h>, since the latter is going away soon.

Prefix the names of members of _RuneLocale and its sub-structures
with ``__'' to avoid polluting the namespace. This doesn't change the
documented rune interface at all, but breaks applications that accessed
_RuneLocale directly.

Use a binary search to find the range containing a character in
RuneRange arrays. This is much faster when there are hundreds of
ranges (as is the case in UTF-8 locales) and was inspired by a
similar change made by Apple in Darwin.

o Merge <machine/ansi.h> and <machine/types.h> into a new header
called <machine/_types.h>.
o <machine/ansi.h> will continue to live so it can define MD clock
macros, which are only MD because of gratuitous differences between
architectures.
o Change all headers to make use of this. This mainly involves
changing:
#ifdef _BSD_FOO_T_
typedef _BSD_FOO_T_ foo_t;
#undef _BSD_FOO_T_
#endif
to:
#ifndef _FOO_T_DECLARED
typedef __foo_t foo_t;
#define _FOO_T_DECLARED
#endif

Concept by: bde
Reviewed by: jake, obrien

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

Megre XPG4 code into libc

Fixed longstanding namespace convolution involving rune_t vs wchar_t.
If _ANSI_SOURCE or _POSIX_SOURCE is defined, then <ctype.h> had to
be included before <stddef.h> or <stdlib.h> to get rune_t declared.
Now rune_t is declared perfectly bogusly in all cases when <ctype.h>
is included.

This change breaks similar (but more convoluted) convolutions in the
stddef.h in gcc distributions. Ports of gcc should avoid using the
gcc headers.

Remove half-dancing solution for signed chars to help finding
POSIXly-incorrect programs.

Move more stuff out to XPG4
Handle negative chars inside runetype/tolower/toupper

Migrate from XPG4 to XPG3 (libxpg4 will be added soon)
Remove big part of my startup_setlocale hack.
Add missing manpage links.

Make not-so-space-eaten locale version:
split modules to bring only neccessary functions,
eliminate sprintf, make reduced startup_locale version.