Author: Petr Škoda
MDL-39430 encourage admins to use opcache extension
http://git.moodle.org/gw?p=moodle.git;a=commit;h=8e0ba6aa4c0fb7a93958e7107c22704e5fd3176a
http://github.com/moodle/moodle/commit/8e0ba6aa4c0fb7a93958e7107c22704e5fd3176a
+ 2.6 en [opcacherecommended,core_admin]