package names and consistency

[Marc Espie <espie_(_at_)_schutzenberger_(_dot_)_liafa_(_dot_)_jussieu_(_dot_)_fr>]

I'm thinking more and more that we want a slightly more standard form
for package names.

Specifically, all packages should have a version number, identifiable as
the -[0-9][^-]*  pattern in the package name.

The version number itself can have wide variations. The only real
constraint is that it can not contain a dash. The next dash triggers
flavors.

Having packages without a version number is a problem, because it's the
only anchor point for parsing the package name (and potential flavors).

We do provide some partial support for packages without version number,
but I don't see why it's a good idea.