using deprecated type in memcacheCache.php

[alexvdp]

the type: cachedump
has been removed from the memcache daemon due to security reasons.

http://php.net/manual/en/memcache.getextendedstats.php

it is still used in the code (line 86) and will give notices like:
Message: MemcachePool::getextendedstats(): Server 127.0.0.1 (tcp 11211, udp 0) failed with: Network timeout (0)