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)

. style(9)
. fix/add comments (to cover changes done thru last 20 months)
. extend monetary testcase to cover int_* values

Fixes to locale code to properly use indirect pointers in order to prevent
memory leaks (fixes bugs earlier purported to be fixed).
Submitted by: Ed Moy <emoy@apple.com>
Obtained from: Apple Computer, Inc.
MFC after: 2 weeks

Rewrite locale loading procedures, so any load failure will not affect
currently cached data. It allows a number of nice things, like: removing
fallback code from single locale loading, remove memory leak when LC_CTYPE
data loaded again and again, efficient cache use, not only for
setlocale(locale1); setlocale(locale1), but for setlocale(locale1);
setlocale("C"); setlocale(locale1) too (i.e. data file loaded only once).

Style fixes in preparation of code rewritting

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

Back out recent replacement of LC_MESSAGES file with directory.

Requested by: ache

Slightly re-work locale messages storage scheme. Before this commit
LC_MESSAGES related data was installed to <locale>/LC_MESSAGES file.
Now it go to <locale>/LC_MESSAGES/SYS_LC_MESSAGES file. LC_MESSAGES
directory is supposed to be storage of message catalogs of userland tools.
This should allow us to avoid many potential problems with future
libintl related functionality introduction.

Thanks for useful suggestions about correct way how to replace plain
files with directories at installworld stage to: Ruslan Ermilov <ru>

* Add my e-mail to copyrights
* style(9)'ify

Fix visibility of empty variable -- it should be static.

Submitted by: bde and Hartmut Brandt <brandt@fokus.gmd.de> (via PR)
PR: bin/25308

catch up to __part_load_locale() interface change

Make comparsions more clear (per style(9))

o Fix build of libc broken in revision 1.2. offsetof() requires the
inclusion of stddef.h.

Reviewed by: peter

Don't use hardcoded struct size, use offsetof() instead (make size calculations
dynamic)

Make FreeBSD locale support complete: add support for rest locale categories
LC_MONETARY, LC_NUMERIC and LC_MESSAGES. Remove stub functions since they
don't need anymore.

Reviewed by: silence on -i18n