SkyLight Detection with cLineBlockTracer

[xoft]

The only problem with light is that it may go out of sync with the world contents for short whiles - when the player places blocks, for example, the light is not recalculated immediately; it will be recalculated on a different thread in a little while. So it is possible for the light values to actually be wrong. I don't think it matters for most practical purposes, just be aware of that