Oddly no cb is fired on close(), work around this.

    Seems funny that connectionpool.connect takes a cb, but pool.close doesn't.
    /me shrugs
Just use one client. Fix emailInfo null check.

    * We used a separate createClient with mysql--I don't see the value here,
      and it seems to have been part of the bug preventing signup flow.
    * The emailInfo null check was barfing because of an attempt to use the
      null uid to look up the passwd hash, causing calamity and consternation.
helenus fail. need to try another client :-(
Change C* driver: helenus -> node-cassandra-cql3.

    This is unfortunate, but we have good reasons:
    * Helenus cannot properly detect boolean or date types. Instead it
      passes everything to CQL as a string. So, if you use any types
      in your schema other than varchar, you'll get errors when inserting.
    * Helenus cannot deserialize compound types (lists/maps/sets), so you
      have to write your own function to convert a raw Buffer. Suck.
    * Helenus' client.close() method doesn't take a callback, instead fires
      an event. This is just one more annoyance to account for if we move back.

    Adding another wrinkle, the new driver does not support node 0.8.
    We'll see how it works out.