Author: Frederic Massart
MDL-48266 backup: Validate backup_auto_storage config
http://git.moodle.org/gw?p=moodle.git;a=commit;h=9fdf16a0fcbb1edd7472151955817993fbb18db0
http://github.com/moodle/moodle/commit/9fdf16a0fcbb1edd7472151955817993fbb18db0
+ 2.9 en [backuperrorinvaliddestination,core]
+ 2.9 en [backupsavetohelp,core]