SDL1.2 is dead, long live SDL

to avoid a crash

Should now ignore all motion events and not warp the mouse when the
window is out of focus.

Fixes Furyhunter/SRB2#1 but probably makes mouse speed too slow on
Linux. Whatever.

-softblit uses SDL2 software renderer backend for blitting

SDL_UpdateTexture is apparently not good for streaming textures.
So instead, I did SDL_LockTexture/Unlock.

GL_EXT_texture_filter_anisotropic is cool I guess

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.

This is a massive performance boost on slow processors, because
before, the intermediary buffer had to be swizzled to ABGR8888
before being uploaded -- for large resolutions this was an
enormous performance penalty.