Merging package does not consider UNKNOWN version stubs

[wagoodman]

Today the pkg.Collection can merge packages that have the same package ID, which is based on the values within all fields on pkg.Package recursively. The downside with this approach is that it does not allow for packages that with UNKNOWN versions to be merged with other packages found by other catalogers which might have more accurate information (e.g. binary cataloger vs go binary cataloger). The reason why package cannot be merged today is because the IDs are guaranteed to be different, since the version field is one of the fields that affects the package ID and the versions in this scenario are guaranteed to be different.

Should we attempt to merge packages in this way?