No need for use_greenlets option in PyMongo 3.
Monitor should store a ClusterSettings.
Temporarily port MongoClient._send_message_with_response to new MongoClient.
Remove command() stub. Prototype read preference implementation.
Test cluster.open().
Unused import.
Dead code in ClusterDescription.
Improve test coverage for Cluster and ServerDescription.
Rename Monitor.open to Monitor.start.
Monitor uses internal methods to check server.