Git commits in Moodle 2.2.4 by ISHIKAWA Takayuki

commit 81bf2a1a1d308ae49062a0c5f821596273996566
Author: ISHIKAWA Takayuki <rechka_osaka@yahoo.co.jp>
Date:   Thu, 14 Jun 2012 20:29:33 +0800
Tag:    v2.2.4

MDL-33757 gradebook: Adding support to sort userlist by email address