msvc: do not compile sample programs for miniupnpc and libpng.
msvc: remove some remnants of SDL and DSound from projects and general cleanup.
windows: make failure to load hid.dll or bthprops.cpl not pop a msgbox, and not crash
msvc: get UnitTests compiling

Choose it from VS or pass /p:RunUnitTests=true to msbuild
Merge pull request #920 from shuffle2/msvc-gtest

Provide a way to build and run unittests on Windows