Ada subtypes and base types

[Robert Dewar]

Laurent GUERBY wrote:

> You keep saying "brain damage", but please if you see a better design
> (other than "forget about user range types" :), let us all know!

Actually I think everyone agrees on what is appropriate here. it is
a matter of working out a clear view. I don't think there are any
real disagreements, just some communication and documentation issues.
(as well as making sure we don't lose conversions we need!)