Author: Sam Hemelryk
MDL-44711 navigation: improved expandable course calculation
http://git.moodle.org/gw?p=moodle.git;a=commit;h=82358535df78ff5f4ece6b975497907659d5713e
http://github.com/moodle/moodle/commit/82358535df78ff5f4ece6b975497907659d5713e
+ 2.6 en [cachedef_navigation_expandcourse,core_cache]