Improve initial block world lighting

[kpreid]

Block worlds have no light initialization (as of commit 612e8c315558baa5b81fa580b98d97bc96b65aa9). Furthermore, their geometry is often such that there are few reflections, so it doesn't fix itself quickly.

There should be an explicit initialization of the light in generated block worlds, perhaps to the outside light level; or, block worlds should have no lighting.