RUBY-565 adding support for ssl cert validation

* Added new SSL options to MongoClient, MongoReplicaSetClient and MongoShardedClient.
* Added SSL certificate check to SSLSocket.
* Updated pool tests to support these changes.

The MongoDB auth spec explicity does not include any of these new SSL values (mostly because they're file paths) so there were no changes required the URI parser. SSL cert validation options must be set directly on the client.