Author: Sam Hemelryk
MDL-44711 navigation: improved expandable course calculation
http://git.moodle.org/gw?p=moodle.git;a=commit;h=cbd063f4c3133b330a0d27c9a0185343d3f3c740
http://github.com/moodle/moodle/commit/cbd063f4c3133b330a0d27c9a0185343d3f3c740
+ 2.8 en [cachedef_navigation_expandcourse,core_cache]