tree-ssa branch: Call for preliminary testing

[Daniel Berlin]

>
> BTW, I haven't tried SSAPRE. Is the implemenation complete now?
The implementation has been complete for a while (though it doesn't do 
load PRE or store PRE yet), it's waiting till overlapping live ranges 
are allowed, because we can sometimes generate them.
I also need it to enable strength reduction.
However, I can bootstrap with SSAPRE enabled.
--Dan