Author: Sara Arjona
MDL-65809 environment: mbstring extension required
http://git.moodle.org/gw?p=moodle.git;a=commit;h=c66e551c1189b1b7031788d9c89af85d8f6eeebb
http://github.com/moodle/moodle/commit/c66e551c1189b1b7031788d9c89af85d8f6eeebb
+ 3.6 en [mbstringrequired,core_admin]