Demonstrate the comparator serialization error in scala 2.10 when using order.reverse

Per issue mentioned in https://github.com/twitter/scalding/issues/505 and  https://groups.google.com/forum/#!topic/cascading-user/ADeupogU6wM, I added a unit test here to demonstrate the issue. I feel this may be more related to a Scala problem...

When ord.reverse is used as a comparator in PriorityQueue, the outer alias in comparator (an Ordering object) in Scala 2.10 doesn't get serialized by Kryo. It seems that this field is considered as a synthetic field in Scala 2.10, so Kryo ignores this field during the serialization. However, this doesn't happen in Scala 2.9.3. Test passes in Scala 2.9.3.