SSA backend

[Stephen Weeks]

> Well, that was deceptively simple.  There was one error in the porting of
> the translation of overflow primitives from x86-mlton.fun to
> x86-translate.fun. 
...

Most excellent.  I'm glad you found it.  It would have taken me days.

> Anyways, I got through all the regressions and am looking at a
> self-compile now.  If the resulting G1 can get through the regressions and
> benchmarks, I'll check it all in.

I just made it through all the regressions and a G2.  I'll merge in the branch
as soon as we get the CVS problem fixed.