Incorrect Sky Light (Non)Updates

[kvverti]

(0.3.1b)

This is persistent after further lighting updates and relog.

Sky lighting under certain conditions will not update to its correct values. Using this simple procedure, one can easily reproduce the bug (Pictures below). As well, sky light and deep vertical shafts have updating problems in general.

In summary, the lighting engine doesn't seem to properly override sky light values when sky light is updated (first pass not overriding existing lighting properly?).

1. Dig a 1x1 hole in the ground (this hole can be of any depth)
2. Place a block above the hole, not filling it but blocking light to the hole.
3. Break the block.
4. Dig down in the hole. Light will decrease even though the hole is open to the sky.

[cuchaz]

Started looking into this today. I think I know what's causing it. I'll see if I can fix it.