Merge remote branch 'public/memcached-expire-stat'

* public/memcached-expire-stat:
  [box] Enable accidently disabled expire in memcached mode.
  [box] Repair memcached statistic. 	* Enable statistic collection. 	* Add counter of expire rate.
  [core] Better param name in stat_register()
  [core] Fix bug causing last stat value being ignored.