Allow specific roles to view unpublished images via a new permission

All of my site image nodes are unpublished because they are only used with image_attach or img_assis inside other pages. This is working well.

However, I need to grant authority for content writers and moderators to be able to view the unpublished image nodes. Giving them 'administer nodes' is too dangerous as it gives much more authority than they should have. Hence I have written a modification which creates a new permission 'view unpublished images' and uses it in image_access() with a new $op case of 'view' to return the correct result to node_access()