The most recent version of the semver repository has fixed a few bugs in version requirements that it rejects. If we update to it, however, it causes breakage, so we had to revert the recent update.

Looks like the semver crate has fixed bugs recently to support new version requirements with build metadata.

I think what we'll need to do is to add a strategy like this where we continue to parse old version requirements, but warn about them.

@steveklabnik, could you add a feature to the semver crate to support old version requirements like 0.2*? Once we do that we can update Cargo to using that, warn about old broken requirements, and start picking up bug fixes.