Author: Andrew Nicols
MDL-59890 calendar: Exporters support for categories
http://git.moodle.org/gw?p=moodle.git;a=commit;h=5ba6507e5b7bdb4bcff325b1f7fd67b7fde0d45c
http://github.com/moodle/moodle/commit/5ba6507e5b7bdb4bcff325b1f7fd67b7fde0d45c
+ 3.4 en [eventnameandcategory,core_calendar]