[m-users.] Issues when upgrading from 2019-07-18 to 2019-10-16

[M McDonough]

> I am open to feedback as to whether it would be worthwhile to add an option
> to stop the generation of the interface file only for errors, and not for warnings.
> Note that such an option would be useful only for projects that do *not* intend
> to fix warnings.

Ohhh...I see. So I should have been doing these imports in the
implementation rather than the interface all along. That makes sense.
It would be nice if the documentation on writing libraries in Mercury
mentioned this :)