Adding support for Windows 8.1 store applications.

Issue was the CRT was split into desktop and store dlls in Visual Studio 2013.
The fix is to set the correct path for the libs when targeting store.

Running Boost tests against 8.1 applications, needs more work.
Basically requiring the app CRT dll to be copied over to the local test folder
and then stripped of the app container requirement like the others. This changes
at least enables the product portions of Boost for 8.1.