RSSA backend

[Matthew Fluet]

> > Why am I plagued with inexplicable regression errors?  
> > 
> > Alright, it only seems to crop up when running in the regression script.
> 
> I just checked out the main trunk and used an NJ compiled G0 to run
> the regression script on {array,callcc,fft,filesys,world1} without
> problems, on all three of our linux machines here.  I have no idea
> what's going on.

What I've found out:
1. The code tagged pre-rssa-merge when compiled with a compiler compiled
from the HEAD sources does not exhibit the bug
2. The HEAD sources does exhibit the bug, both when compiled with a
compiler compiled from the HEAD sources and with a compiler compiled from
the pre-rssa-merge sources
3. The bug only occurs when the compiler is run from within the regression
script.
4. Furthermore, the bug does not occur when the regression script only
compiles the files that have otherwise been causing the problems.

Ah, I just figured it out.

Hint: bash programs are _not_ lexically scoped.