title: Redis multi with bluebird promises
body: <p>Do you know a way for using redis client's multiple transactions command with bluebird promises?</p>
  
  <p>Because, the following code never finishes.</p>
  
  <pre><code>  var $redis = require('redis'),
        $p = require('bluebird'),
        $r = $p.promisifyAll($redis.multi());
  
    $r.setAsync('key', 'test')
      .then(function(reply, data) {
        // ...
      });
  
    $r.exec(function() {
      $r.quit();
      process.exit();
    });
  </code></pre>