There were two indexed images with transparency that became messed up with the new SDL_image. I'm not sure why but I resaved them as non-indexed in GIMP, they grew a bit but now look fine.
Also replace savepng with SDL_image's IMG_SavePNG.
Assumedly abbreviation of "global illumination", some kind of alternative to the current way of drawing the shadows. Doesn't work very well when enabled, remove it.
Android now uses the JPEG textures that the PC version used, instead of the ETC1 encoded images in `data-mobile`. ETC1 texture loading is also removed as it is now unused.