Check for the existance of the pages book before updating the books, thumbnail,
as pages may be ingested before the book.
Merge pull request #57 from nigelgbanks/7.x-derivative-fail-if-book-is-not-present

Check for the existance of the pages book before updating the books, thu...
Only select active pages.
Merge pull request #58 from adam-vessey/7.x-VC-5

Only select active pages.