[m-rev.] for possible review: make ':- external' a pragma

[Zoltan Somogyi]

On Wed, 22 Jul 2015 13:30:46 +1000 (AEST), Julien Fischer <jfischer at opturion.com> wrote:
> The diff looks fine.  Are you intending to remove the ':- external'
> variant at some point?

We need to wait for

(1) this diff to be installed, and then
(2) replace all uses of `:- external' with the new pragmas, and
only then can we
(3) remove support for `:- external'.

Steps 2 and 3 both break the ability to build the compiler with an old
installed compiler. I would prefer to stretch this out over several months;
there is no hurry. But yes, eventually, there will be no need for `:- external'.

Thanks for the review.

Zoltan.