Include windows.h in a single point in the source, so we can be consistent about the definition of UNICODE and have core utility functions for Windows that all modules can share.

I think this also fixes the bug relating to non-latin characters in filenames, since UNICODE wasn't defined in SDL_rwops.c

--HG--
rename : src/SDL_android.cpp => src/core/android/SDL_android.cpp
rename : src/SDL_android.h => src/core/android/SDL_android.h