JAVA-851: disable check for upper bound on chunkSize in GridFS
JAVA-853: Properly handling nested calls to DB.requestStart/requestDone by keeping tracking of the nesting depth, and only removing the thread local when the depth returns to 0.
JAVA-812: Only set $readPreference on a query if the read preference is not primary.
This lets the slaveOK bit have precedence if it's set.
JAVA-790: Change index options from {unique: 1} to {unique : true}
JAVA-872: Set alwaysUseMBeans in MongoOptions(MongoClientOptions) constructor.  See writeConcern to null in MongoClientOptions.reset() and MongoClientOptions.copy()