As mentioned in #733, Local overrides via .cargo/config path = [ "foo" ] override all dependencies with the same name, even if they have different versions.

This contrasts the behavior when a project with a dep on one version of a library (A) also depends on anther lib (B) that pulls another version of the library A. In that case, both versions are included in the build.

Given the above, it will probably be useful to allow overrides on a finer grained basis.