code: function(ferret, collection_name, callback) {
      _ready(ferret, function(err) {
          if (err) {
              process.nextTick(function() {
                  callback(err)  
              })
          } else {
              if (ferret._collections[collection_name]) {
                  process.nextTick(function() {
                      callback(null, ferret._collections[collection_name])
                  })
              } else {
                  ferret._db.collection(collection_name, function(err, collection){
                      if (!err) { ferret._collections[collection_name] = collection }
                      callback(err, collection)
                  })
              }
          }
      })
  }
docs: Try loading a collection from the cache. If that fails, get it from the driver