Author: Petr Škoda
MDL-34853 use new duration setting type in enrol_paypal
http://git.moodle.org/gw?p=moodle.git;a=commit;h=ef2737a4df77ef4d34978932f78514f40e40252e
http://github.com/moodle/moodle/commit/ef2737a4df77ef4d34978932f78514f40e40252e
+ 2.4 en [enrolperiod_desc,enrol_paypal]