Blocks and portals, what more do ya need?

I did an incomplete Minecraft clone a ways back (see 'Voxels'), and I've been wanting to 
start anew and make a better one. I've also always wanted to try implementing portals.

GPL v3
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Some random details:

Portals are done in roughly the same way as Portal (via stencil masks, rather than RTTs).

The Minecraft-style stuff is done similar to how Minecraft seems to work, but I've 
multithreaded most of the demanding parts of the calculations, so it should stay 
fairly smooth; though this adds a lot of complications with accessing chunk data.

It's sort of a hacky mess, but whatever...