Author: Petr Skoda
MDL-46660 muc: add env check to memcache driver
http://git.moodle.org/gw?p=moodle.git;a=commit;h=67dabb5ace3e371ce02e121e13feb68bb9f1d49d
http://github.com/moodle/moodle/commit/67dabb5ace3e371ce02e121e13feb68bb9f1d49d
+ 2.8 en [memcacheversioncheck,cachestore_memcache]
+ 2.8 en [memcacheversionwarning,cachestore_memcache]