link validation / deactivation mechanism via cron

It would be useful to have an administration command or cron command that would verify all links and mark invalid links.

Any links marked as invalid would not be published.

Invalid links would eventually be re-validated by the admin/cron and marked as such, allowing them to be published if they were marked as published.

Possibly have a "delete invalid links after verification attempts" that would expunge links as appropriate.

Note that marking as invalid is an important distinction because it's neccessary to be able to manually mark as unpublished without having the link be re-published when the cron command confirms the link is still valid.

Thanks,
Eric Cosky