Fixed warning on 32-bit

- Fullscreen enum variant gave a `literal out of range for its type' warning
Merge pull request #123 from mvdnes/enum-literal

Fixed warning on 32-bit
c_schar is no longer in libc base export
Forgot one c_schar in sdl_image
Merge pull request #125 from mvdnes/schar_moved

c_schar is no longer in libc base export