book_manager fails to batch update

I think this may be an issue with php 5.3+, but I'm really unsure

Parameter 2 to og_book_manager_batch_operate() expected to be a reference, value given in /srv/www/www.threeclicks.org/public_html/sites/all/modules/contrib/book_manager/book_manager.batch.inc on line 52.

Attached patch resolves the issue.