upset and setup.ini change for the next version

[Robert Collins]

I've nearly completed the code that will do different requires: clauses
per version of a package.

The reason is to allow new dependencies to be introduced with a new
version of a package, but not affect folk who don't upgrade the package.
It's also a precursor to embedded metadata.

However, setup.ini now needs a requires line statement for each
version - ie
[Prev]
Requires:
..

Chris, can upset handle this now?

Rob