Author: Ankit Agarwal
MDL-27884 Implement proper username validation during csv import
http://git.moodle.org/gw?p=moodle.git;a=commit;h=7bf99ee558856ebdc8b2da58b5b61d43da339b00
http://github.com/moodle/moodle/commit/7bf99ee558856ebdc8b2da58b5b61d43da339b00
+ 2.5 en [invalidusername,core_error]