Author: Sam Hemelryk
MDL-34398 groups: implemented caching of group information.
http://git.moodle.org/gw?p=moodle.git;a=commit;h=e17dbeeb1a0eeada466350a621ce0adc2a03b596
http://github.com/moodle/moodle/commit/e17dbeeb1a0eeada466350a621ce0adc2a03b596
+ 2.5 en [cachedef_groupdata,core_cache]