for review: allow `any' insts as non-local vars in higher-order terms

[Andrew Bromage]

G'day all.

Fergus Henderson wrote:

> Comments, please?
> Andrew, is this OK with you?

Seeing as we have to revisit this stuff sooner or later anyway, and
playing with `any' isn't actually unsound in our implementation, we
might as well do this now.

However, I think you should also add some documentation to the definition
of freeze to say that the idiom may be revisited at some point in the
future.

> compiler/modecheck_unify.m:
[...]
> 	Andrew's change as correct, but unfortunately it breaks most
                        ^^ Typo

> Index: modecheck_unify.m
> ===================================================================
[...]
> @@ -373,8 +373,11 @@
[...]
> +	% For the moment, since doing all the properly seems too hard,
                                      ^^^^^^^^^^^^^^^^ Ditto

Cheers,
Andrew Bromage