Improve performance on personal outline page

Right now, if the user doesn't have 'administer nodes' rights, we do a node_load() on every node in the book to see if we should put out an Edit and/or Delete link.

The 2.x branch is taking a more pure approach to the personal book, so it can be assumed that every node in the book is owned by the book's author. So we can remove all those node_load() calls and just give them the Edit and Delete links. They'll still get caught later on in the process if someone clicks them and they don't have rights to edit or delete; and, if this isn't the desired behavior, a custom module can change the way this works.