Author: Frederic Massart
MDL-28346 Backup: Backup does not fail when a file is missing
http://git.moodle.org/gw?p=moodle.git;a=commit;h=a173b52da0765ecc39119b74d7579baf650470ec
http://github.com/moodle/moodle/commit/a173b52da0765ecc39119b74d7579baf650470ec
+ 2.4 en [missingfilesinpool,core_backup]