Content creators with appropriate permissions can create and edit unpublished book pages and outlines

This patch addresses a usability issue with Drupal's book module since 2005 😵.

In the past, content creators could not create or edit draft (unpublished) book pages.
A book page needed to be published to be appear in the book menu tree.

This did not suit most organizations’ creation and editorial review workflows.

With this patch, content creators with the appropriate permissions:
'create new books',
'create book content',
'edit own book content',
'add content to books',
'access printer-friendly version',
'view any unpublished content'
can now prepare unpublished book pages, review and edit them, and then publish them when appropriate.