Author: Marina Glancy
MDL-37812 user: added defaults for user preferences
http://git.moodle.org/gw?p=moodle.git;a=commit;h=747dac69f90c59a6ebfdc58901e4fbfdae318ece
http://github.com/moodle/moodle/commit/747dac69f90c59a6ebfdc58901e4fbfdae318ece
+ 2.8 en [userdefaultpreferences,core_admin]