Abstracted ReplicaSetMongoConnection into two classes and an interface:  The interface is MultipleServerConnectionStrategy and the implementation is ReplicaSetConnectionStrategy.  ReplicaSetMongoConnection is now MultipleServerMongoConnection, which delegates to MultipleServerConnectionStrategy the task of choosing the address of the primary (for writes) or whichever server should handle the given read preference (for reads).

This paves the way for a MongosSetConnectionStrategy class.