ReplicaSetConnection.close() doesn't close connection

See: https://gist.github.com/92e4b1fd8485ab9008f7

4 threads are run, each creating a ReplicaSetConnection to connect to a replica set with 2 secondaries and 1 master. Each hour, the threads reconnect by gc'ing the existing connection and creating a new one. mongodb shows the connection count rising, which causes an out of file-descriptor error after an extended period of time.