[m-dev.] diff for review - bug fix

[Simon TAYLOR]

Hi Fergus,

> Your changes look fine, but I don't understand how the bug you
> fixed could cause an abort.  It looks like before the bug fix,
> we just didn't do as good a job of dead procedure elimination
> as we could have - but I don't see how that could cause
> an abort, unless there is another unfixed bug somewhere else.
> 
> So could you please explain it to me?

The problem was that the unification procedure was inlined, so
it wasn't used any more, then unused_args.m created a new version 
since the type_info argument was unused. Dead procedure elimination was
working out that both procedures were unused, but only the unused_args
version was actually removed due to the bug fixed by the diff. This
left the old version calling a non-existent procedure, and simplify.m
aborted.

Simon.