Lights are not updated properly on block removal

[kpreid]

When a block is removed, it and its neighbors' light levels are updated, but the absence of the block means that a different set of rays are cast; this results in light or shadow that should go away not doing so.

A brute-force solution would be to, when a block is replaced, cast a full set of rays from it and its neighbors and add all the hits to the lighting update queue.