[Yt-dev] Projection speed improvement patch

[Matthew Turk]

> dang it.  This looks like I'm just passing around arrays that are too
> big.  I think for this I might need some help from other people about
> the right way to do this...  Ideas, anybody?

Hm, at the risk of replying to my own message, we might be able to do
this by using a memmap onto the disk.  But then we'd be assuming
homogenous clusters, which honestly, I think we should just go ahead
and assume.  But I'd rather keep things off the disk if at all
possible.  I suppose when we're dealing with arrays of this size,
though, it does become a bit prohibitive...

-Matt