Remove compiler warnings
Remove the unused function WelsSleep

Windows Phone 8 doesn't have Sleep(), but there's no need to
use the function at all.
Use more modern versions of functions that don't exist on Windows Phone
Use the Windows Runtime ThreadPool API for creating threads on Windows Phone

Windows Phone lacks the old CreateThread/beginthreadex APIs for
creating threads. (Technically, the functions still do exist,
but they aren't officially supported and aren't visible in the
headers when targeting Windows Phone.)

Building code that uses the Windows Runtime language extensions
requires building with the -ZW option.
Explicitly request 2 threads when testing slice threading

Previously the default value of iMultipleThreadIdc was 0,
which made sure threads were used for the test with multiple
slices (if run on a multicore machine). Now the default is 1,
so multiple threads has to be requested.

Explicitly request 2 threads, to make sure the threading code is
tested, even on machines with only one core.
Remove the now unused MT_ENABLE define from project files
Merge pull request #614 from mstorsjo/remove-unused-define

Remove the now unused MT_ENABLE define from project files
Merge pull request #610 from mstorsjo/wp8-threads

Make threading work on windows phone
Merge pull request #598 from varunbpatil/compiler_warnings

Remove compiler warnings
Merge pull request #611 from mstorsjo/test-multithreading

Explicitly request 2 threads when testing slice threading