-memcached_delete() is used to delete a particular key. An expiration value
-can be applied so that the key is deleted after that many seconds, but this
-will only work if you are using a 1.2.x server. If you are using a 1.2.x
-server and you want to use the expiration value, please call memcached_version
-one time for the memcached_st instance. If you don't do this no-reply and
-buffered mode will be disabled to avoid getting out of sync with the server.