SERVER-15564 Send config version and member ID with every replSetUpdatePosition command and use the given member ID if there hasn't been a handshake
SERVER-14734 Send exactly one replSetUpdatePosition command upstream per replSetUpdatePosition command received
SERVER-15565 Prefer member IDs to RIDs for identifing secondaries for tracking replication progress
SERVER-15565 Avoid iterating _slaveInfo when updating member optimes based on heartbeat response