Author: Sam Hemelryk
MDL-25290 cache: Added cache locking plugin and converted locking implementations to that
http://git.moodle.org/gw?p=moodle.git;a=commit;h=34c84c723a7f8cc365cbdc82d339fb59016ccbf0
http://github.com/moodle/moodle/commit/34c84c723a7f8cc365cbdc82d339fb59016ccbf0
+ 2.4 en [pluginname,cachelock_file]
+ 2.4 en [ex_nodefaultlock,cache]