Unpublish latest revision

Hi,

I've made my "page" content type to be unpublished by default and I have two roles, "author" that can create pages (and cannot publish them) and "editor" that can publish/unpublish pages, and it works as expected.

When the editor reviews a page and publish it, the author can still edit it, thus creating a new revision (that would be shown and published). I would like drupal to not use this latest revision but only the one the editor published. Because the editor would have to review this newer revision before making it available.

Any idea how can I do that? How can I instruct drupal to not automatically publish any new revision? (partial and work-around solutions also accepted :p)

Thank you in advance!