Merge from libarchive.googlecode.com: Mostly a bunch of
corrections to the Windows support to reconcile differences
between Visual Studio and Cygwin. Includes parts of
revisions 757, 774, 787, 815, 817, 819, 820, 844, and 886.

Of particular note, r886 overhauled the UTF-8/Unicode conversions to
work correctly regardless of whether the local system uses 16-bit
or 32-bit wchar_t. (I assume that systems with 16-bit wchar_t
use UTF-16 and those with 32-bit wchar_t use UCS-4.) This revision
also added a preference for wcrtomb() (which is thread-safe) on
platforms that support it.