Author: Cameron Ball
MDL-35104 auth: Don't allow modification of username
Presently it is either unreliable, or not possible to change
the username of a user created with an authentication plugin.
In some cases it is even hard coded to fail. Ideally we would
sync the username, and the issue MDL-21928 exists to address
that. However, in the mean time we should not allow the
username of an external user to be modified.
http://git.moodle.org/gw?p=moodle.git;a=commit;h=34d728d3e93031dfb52146ec1f820e152ab28fd3
http://github.com/moodle/moodle/commit/34d728d3e93031dfb52146ec1f820e152ab28fd3
+ 3.1 en [username,core_auth]
+ 3.1 en [username_help,core_auth]