Author: Jeremy Schulz
MDL-80605 uploaduser: fixed username already existing when mail-matching
http://git.moodle.org/gw?p=moodle.git;a=commit;h=fbbb39ca6281556ab6e5dc69ea8e6eb7e7410cf4
http://github.com/moodle/moodle/commit/fbbb39ca6281556ab6e5dc69ea8e6eb7e7410cf4
+ 4.2 en [usernotaddedusernameexists,core_error]