sdl2: reorder graphics initialization

GL Initialization needs to happen before window creation,
otherwise the GL library will get reloaded while in use and
Windows will have a heart attack. This is bad, obviously.
Merge remote-tracking branch 'Furyhunter/sdl2' into sdl2
sdl2: fix mouse motion (remove -mousewarp)
sdl2: restore anisotropic filtering support in gl
sdl2: handle no AF support correctly (1, not 0)

GL_EXT_texture_filter_anisotropic is cool I guess
sdl2: limit fullscreen resolution in OpenGL
sdl2: potential huge perf. boost to software

SDL_UpdateTexture is apparently not good for streaming textures.
So instead, I did SDL_LockTexture/Unlock.
Merge remote-tracking branch 'Furyhunter/sdl2' into sdl2