uqm: Switch to building with SDL2

Version 0.8.0 finally has support for SDL2 and thus much better support
for multiple monitors. While I'm currently on my crap^Wlaptop, I can't
test support for it, however when trying UQM with SDL1 it wasn't even
able to create a window:

Couldn't set OpenGL 800x600x32 video mode: Couldn't find matching GLX visual
Couldn't set OpenGL 800x600x24 video mode: Couldn't find matching GLX visual
Couldn't set OpenGL 800x600x16 video mode: Couldn't find matching GLX visual
Couldn't set any OpenGL 800x600 video mode!
Could not initialize video: no fallback at start of program!
Do not know how to display an error box

SDL2 on the other hand works like a charm and it also scales properly
when you resize the window (one thing that has annoyed me with the SDL1
version in the past).

Signed-off-by: aszlig <[e-mail]>

pkgs/games/uqm/default.nix

···
 { stdenv, lib, fetchurl, fetchFromGitHub, pkg-config, libGLU, libGL
-, SDL, SDL_image, libpng, libvorbis, libogg, libmikmod
+, SDL2, libpng, libvorbis, libogg, libmikmod
 
 , use3DOVideos ? false, requireFile ? null, writeText ? null
 , haskellPackages ? null
···
   };
 
   nativeBuildInputs = [ pkg-config ];
-  buildInputs = [ SDL SDL_image libpng libvorbis libogg libmikmod libGLU libGL ];
+  buildInputs = [ SDL2 libpng libvorbis libogg libmikmod libGLU libGL ];
 
   postUnpack = ''
     mkdir -p uqm-${version}/content/packages