Author: Dongsheng Cai
MDL-29476 web service improvements
1. moodle_enrol_get_users_courses should return number of participants,
2. moodle_user_get_users_by_courseid should limit the fields to be returned
http://git.moodle.org/gw?p=moodle.git;a=commit;h=ad7612f59729a15452c53d70287b9bc3f4db26f6
http://github.com/moodle/moodle/commit/ad7612f59729a15452c53d70287b9bc3f4db26f6
+ 2.2 en [invaliduserfield,core_error]