don't try to override members that are privateWithin anything

[martijnhoekstra]

Pull Request Checklist

• [x] I agree to licence my contributions under the MIT licence
• [x] I have added copyright headers to new files
• [x] I have added tests for any changed functionality

Purpose

When a class have package-private members, we can't override those. This is the case among other things for default access java methods. Check privateWithin to determine whether we can override.

Background Context

References

Are there any relevant issues / PRs / mailing lists discussions?

[goshacodes]

Hi, thank you for your contribution, this one is ready to merge