[m-rev.] for review: deleting :- external

[Julien Fischer]

On Sat, 12 Mar 2016, Zoltan Somogyi wrote:

> The diff is straightforward and does not need review; the review
> is for the idea of removing support of :- external. It has always been
> an implementors-only part of the language, and it has been replaced
> by external_pred and external_func pragmas for several months now.
> Unlike :- external, these are NOT ambiguous.
>
> Does anyone know of any code that uses :- external and which
> hasn't been updated to use the replacement pragmas instead?

No, I'm not aware of any code that still uses it; you can go ahead and
commit this.

Julien.