[WGL] Fix window size calculation.
Merge branch 'master' of git://github.com/libretro/RetroArch
DInput/XInput fixups.

- Fix DInput if XInput failed to load and you're using an XInput device.
- Try to load XInput 1.4 first. It's installed by default on Win8.
- Don't bother checking "system directory" explicitly, it already does.