Fix more shadowing issues - this time shadows inside objects

This should work for all docking tunnels (except the straight-through ones) - so closes #94 - but the glare effect as a whole will need a better way of handling it after 1.80 is out as there are still a bunch of strange cases: straight-through docking tunnels, odd effects around Torus stations and other large "pancake"-shaped objects, and so on.