memcached_dump() is used to get a list of keys found memcached(1) servers.
Because memcached(1) does not guarentee to dump all keys you can not assume
you have fetched all keys from the server. The function takes an array
of callbacks that it will use to execute on keys as they are found.
Currently the binar protocol is not supported.
A value of type "memcached_return_t" is returned
On success that value will be "MEMCACHED_SUCCESS".
Use memcached_strerror() to translate this value to a printable string.