MDL-38147 removed function coursecat::get_all_parents() as ineffective and unnecessary
MDL-38147 Retrieve and cache only often-used fields of course category
visibleold
event-driven cache purging
MDL-38147 replaced function coursecat::get_all_ids() with coursecat::get_tree()
change to cache def
bug fix in caching contexts
bug fix in new cache
get_children