Git commits in Moodle 2.5.1 by Kyle Temkin

commit 11f6680deec05ae45aa563c8956dbd9adf1a0f53
Author: Kyle Temkin <ktemkin@binghamton.edu>
Date:   Thu, 20 Jun 2013 11:31:01 +0800
Tag:    v2.5.1

MDL-40264 fix essay handling of zero-string response