Author: Mark Nelson
MDL-42764 core: added missing string definition
Also changed the string index so it was not
vague. The index 'emailempty' appears as if it
could belong to a validation method for a form.
http://git.moodle.org/gw?p=moodle.git;a=commit;h=ac8bf022147c69809550458c439d1661474c89e6
http://github.com/moodle/moodle/commit/ac8bf022147c69809550458c439d1661474c89e6
+ 3.3 en [emailuserhasnone,core]