SSA backend update

[Stephen Weeks]

> What kind of failures: compile-time (uncaught exception or asserts) or
> run-time (seg-fault or wrong results)?

run-time, mostly wrong results.

> Quite a bit of stuff in the native codegen is under Assert.assert.  In
> particular, all of the liveness checking in between phases of the
> simplifier.  For seg-faults, it's a long and ardous journey with
> -g -keep-pass toMOut -keep g -native-commented {1,...,5}.

OK, I'll compile using an NJ-G0 and start playing with gdb ...