Author: Petr Škoda
MDL-34046 improve mixed files upgrade error
Credit goes to Gordon Bateson.
http://git.moodle.org/gw?p=moodle.git;a=commit;h=fe6d428185e66746d6ebfa61728c6a64e946e8ef
http://github.com/moodle/moodle/commit/fe6d428185e66746d6ebfa61728c6a64e946e8ef
+ 2.3 en [upgradestalefiles,core_admin]
+ 2.3 en [upgradestalefilesinfo,core_admin]