Assorted changes to get specs to green.

1. Clean up memcached processes after creation, so the processes aren't reused.
2. Remove use of the 'second' method on Array (added by ActiveSupport).
3. Fix Travis rbx keys so the specs run under Rubinius (although they fail).
4. Set value on stats spec, so it doesn't depend on server processes from other specs to pass.

Specs are now green on Travis, although the Rubinius specs are still failing.