http://noc.wikimedia.org/conf/highlight.php?file=CommonSettings.php has the following in the configuration for the collection extension:
$wgLicenseURL = "http://en.wikipedia.org/w/index.php?title=Wikipedia:Text_of_the_GNU_Free_Documentation_License&action=raw";
This page indicates: As of July 15, 2009 Wikipedia has moved to a dual-licensing system that supersedes the previous GFDL only licensing. In short, this means that text licensed under the GFDL only can no longer be imported to Wikipedia, retroactive to 1 November 2008. Additionally, Wikipedia text might or might not now be exportable under the GFDL depending on whether or not any content was added and not removed since July 15. See Wikipedia:Licensing update for further information.
I think that we may be creating books with an incorrect license and that it should probably point to CC-BY-SA 3.0 ;).