In MongoClientOptions and ServerSettings, replaced heartbeatConnectRetryFrequency with minHeartbeatFrequency in order to comply with the server monitoring specification.

JAVA-1470
In MongoClientOptions and ServerSettings, removed heartbeatThreadCount property.

JAVA-1479
Mechanism properties for MongoCredential are now case-insensitive

 JAVA-1462
Removed logging of initialization failure, as that should be logged higher up.
Also changed the name of the logger to be the module name rather than the class name, as it is elsewhere.

 JAVA-1459
Removed unused non-public method in DB and unused private static field in DBCollection

JAVA-1416