Key Iterator for memcached,use 'stats items' and 'stats cachedump' to iterate all keys,it is inefficient and not thread-safe.The 'stats cachedump" has length limitation,then iterator could not visit all keys if you have many keys.
Note: memcached 1.6.x will remove cachedump stats,so this feature will be invalid in memcached 1.6.x
@deprecated memcached 1.6.x will remove cachedump stats command,so thisfeature will be removed in the future
@author dennis