lib/common/makeuser.py: When a new user is added (either by hand or by usrmgt), pulls the subject codes from afar and adds enrolments to the DB.
This performs the same function as ./enrolallusers, but does it precisely when the user is created, to avoid having to run enrolallusers just to get new users into subjects (though you still have to run enrolallusers whenever new subjects become available, or if an existing user enrols in new subjects).