repo_autopattern: support creation of obsoletes for product packages

repo_autopattern: support creation of obsoletes for product packages

This adds support for provides of the type "product-obsoletes(name)".
We translate this to "Obsoletes: product:<name>" in the generated
product pseudo package.

We need this because people used "Obsoletes: product:name" in the
"release" package, but this is no longer allowed in newer rpm versions.
Besides, the obsoletes is kind of wrong in the "release" package
anyway, it belongs in the generated "product:" package.