Git merges in Moodle 2.3.9 by Marina Glancy

commit 8d296ea5e4c6787efd10eff767780d8a5fbec575
Author: Marina Glancy <marina@moodle.com>
Date:   Wed, 10 Jul 2013 10:05:16 +0800
Tag:    v2.3.9

Merge branch 'm23_MDL-39832_Fix_Chrome_Issues_ETag_XSendfile_2ndRound' of https://github.com/scara/moodle into MOODLE_23_STABLE