Git commits in Moodle 2.5.4 by James Pratt

commit d8ca0c903c0c034bd704da0f7ca5d845e6dc973a
Author: James Pratt <me@jamiep.org>
Date:   Wed, 27 Nov 2013 13:49:19 +0800
Tag:    v2.5.4

MDL-43079 quiz statistics : fix stats graph when all grades zero