Author: Petr Škoda
MDL-34853 use new duration setting type in enrol_manual
http://git.moodle.org/gw?p=moodle.git;a=commit;h=47c8b9788f53cf080591f33b95bd81dfe7daf5dc
http://github.com/moodle/moodle/commit/47c8b9788f53cf080591f33b95bd81dfe7daf5dc
+ 2.4 en [defaultperiod_desc,enrol_manual]