Git merges in Moodle 2.5.7 by AMOS bot

commit cdc60776d795e7d173f5a2e0135c56c835cca58f
Author: AMOS bot <amos@moodle.org>
Date:   Fri, 11 Jul 2014 08:44:28 +0800
Tag:    v2.5.7

Merge branch 'MOODLE_25_STABLE' into install_25_STABLE