added support for:

added support for:
    - user->policyagreed:
        if the destination server is different, reset it
   - user_students->enrol and user_teachers->enrol
        if not set or the destination server is different, set it to $CFG->enrol
somethings should be modified in the rest of moodle:
    - update all the 'manual' entries to 'internal'
    - modify the enrol_teacher() to use $CFG->enrol by default
    - make every enrol method set this field properly.
    - perhaps, mark metadata users with a new value too.