options for book page authorship

Per: http://drupal.org/node/93678#comment-157302

For much of the 4.7.x release cycle, the "feature" of the book module that reassigns authorship of a book page to the last user to edit it was broken. In the issue above, this bug was fixed, and this is now causing consternation and unhappiness on the d.o documentation team.

This issue is a request to either abolish that code in book_submit(), or add a configuration option to make it optional.