sdl2
- change the windows scancode logic to use the scan code value in lparam rather than VK's to get a stable scancode value across different KB layouts
sdl2
- fix atomic header to compile happily under msvc 6.0
sdl2
- fix ref counting on init, make sure you refcount each init calls and not just the first one
sdl2
- more scancode goodness, removing now dead wparam translation code
- add scancode for SDL_SCANCODE_NONUSBACKSLASH
- don't translate sdl key values for numeric and grave key

CR: SamL
sdl
- fix win32 mapping of alpha-numeric keys after scancode changes
Cleanup of SDL_PrivateShouldInitSubsystem.

Also fixes a build error if a module was disabled.