[m-rev.] diff: simplify handling of foreign_export_enums

[Julien Fischer]

On Sat, 24 Feb 2018, Zoltan Somogyi wrote:

> Would anyone object if I reworded the error messages
> for foreign_enums and foreign_export_enums? Instead of
> talking about mappings between Mercury and foreign languages names
> "not [being] a bijection", I think they should say something along the
> lines of " the mapping is inconsistent", while giving the names of the
> Mercury or foreign names that are mapped to more than one name
> in the other language.

No, go ahead.

Julien.