Author: Frederic Massart
MDL-28346 Backup: Restore does not fail when a file is missing
http://git.moodle.org/gw?p=moodle.git;a=commit;h=3b232aeffb6bc59ba45b47bbbbfeff9479881323
http://github.com/moodle/moodle/commit/3b232aeffb6bc59ba45b47bbbbfeff9479881323
+ 2.4 en [restorefileweremissing,core_backup]