Added AC icon to SDL window (fixes #29)

As zeSKB reported, there was no icon for the game window.
This should now be fixed. We might want to make it transparent in the future,
but we would have to make sure it will be supported by any system.

source/src/main.cpp

@@ -1122,6 +1122,8 @@ int main(int argc, char **argv)
 
     initlog("video: misc");
     SDL_WM_SetCaption("AssaultCube", NULL);
+    SDL_Surface *icon = IMG_Load("packages/misc/icon.bmp");
+    SDL_WM_SetIcon(icon, NULL);
     keyrepeat(false);
     SDL_ShowCursor(0);