Make sure to at least request 4x MSAA
Apply dithering to spotlight.frag

This was used in order to avoid banding artifacts on the plane below the
spotlight. The algorithm is fairly simple: once you have the final color
computed as a float, stochastically choose the nearest quantized value
based on how far away from it you are. In general this seems to produce
pretty good results for 8-bit framebuffers.