book_manager 6.x-2.0

Changes since DRUPAL-6--1-5:

• Updated for 2.x branch.
• #712884 by marcp: Fixed "Undefined property when adding child page" notice
  when adding child node.
  #712588 by FrankT: Fixed some string typos and cleaned up some unclear
  strings.
  #712046 by marcp: Added back the "Add child page" link for the case where
  a site doesn't want individual "Add [content-type]" links for each allowed
  book content type.
• Check to see if book_manager has been initialized in
  _book_manager_is_personal_book().
• #384862 by kleinmp, evoltech, marcp: Allow users to change the titles on
  the personal outline page.
• #714260 by marcp: Improve performance on personal outline page by avoiding
  node_load() on every node in the book when the user doesn't have
  'administer nodes' permission.