Users that can't edit the original post shouldn't see a link to edit it.
- Use correct original post type 'edit_post' cap to determine whether or not current user can edit original. - Temporarily remove `map_meta_cap` preview filter when generating edit links so that actual capabilities are checked. - Switch from `add_action` to `add_filter` for `map_meta_cap`.
Without it `get_edit_post_link()` will misleadingly fall back to global $post
Relies on post meta tracking key instead of alt. versions post_parent Cuts out an unnecessary WP_Query
If post_parent = 0, $this->original was being set to the current global $post