This patch speeds up and reduces the memory usage of SSAPRE.
On one testcase, it went from 100 seconds to 4 on my Macintosh.
It also starts to implement load PRE
Load PRE on non-indirect refs now works (and bootstraps and passes
regtests), but i've disabled it until i get it *all* working at once
(it currently miscompiles stage2 slightly).
I fixed a few bugs along the way that others had pointed out.
We also now keep and print memory statistics.
Bootstrapped and regtested on 686-pc-linux-gnu (and
powerpc-darwin-7.0.0 with a few darwin config changes).