Git merges in Moodle 2.1.5 by AMOS bot

commit 856623590c3ba8f3c1d5dfc9dc6c9f2d500eb0d7
Author: AMOS bot <amos@moodle.org>
Date:   Sun, 08 Jan 2012 08:31:26 +0800
Tag:    v2.1.5

Merge branch 'MOODLE_21_STABLE' into install_21_STABLE