Move memcached back to '3.0' branch

Change-Id: I2ed23706ad4b77fd57bda9b1c597f4e5968e203e
Reviewed-on: http://review.couchbase.org/42926
Reviewed-by: Dave Rigby <daver@couchbase.com>
Reviewed-by: Chris Hillery <ceej@couchbase.com>
Tested-by: Chris Hillery <ceej@couchbase.com>