Author: Sara Arjona
MDL-65809 environment: mbstring extension required
http://git.moodle.org/gw?p=moodle.git;a=commit;h=7bda7e786b5ca2528a29bc880c3aa2f083e1cbc3
http://github.com/moodle/moodle/commit/7bda7e786b5ca2528a29bc880c3aa2f083e1cbc3
+ 3.7 en [mbstringrequired,core_admin]