SDL: cleanup and add patch to discover extensions

pkgs/development/libraries/SDL_image/default.nix

@@ -1,7 +1,8 @@
 { stdenv, fetchurl, SDL, libpng, libjpeg, libtiff, libungif, libXpm }:
 
 stdenv.mkDerivation rec {
-  name = "SDL_image-1.2.12";
+  name = "SDL_image-${version}";
+  version = "1.2.12";
 
   src = fetchurl {
     url    = "http://www.libsdl.org/projects/SDL_image/release/${name}.tar.gz";
@@ -10,18 +11,9 @@ stdenv.mkDerivation rec {
 
   buildInputs = [ SDL libpng libjpeg libtiff libungif libXpm ];
 
-  postInstall = ''
-    sed -i -e 's,"SDL.h",<SDL/SDL.h>,' \
-      -e 's,"SDL_version.h",<SDL/SDL_version.h>,' \
-      -e 's,"begin_code.h",<SDL/begin_code.h>,' \
-      -e 's,"close_code.h",<SDL/close_code.h>,' \
-      $out/include/SDL/SDL_image.h
-    ln -sv SDL/SDL_image.h $out/include/SDL_image.h
-  '';
-
   meta = with stdenv.lib; {
     description = "SDL image library";
-    homepage    = http://www.libsdl.org/projects/SDL_image/;
+    homepage    = "http://www.libsdl.org/projects/SDL_image/";
     maintainers = with maintainers; [ lovek323 ];
     platforms   = platforms.unix;
   };