Revision 1243326

MAHOUT-933: 
- Implemented ClusteringPolicyWritable and made ClusteringPolicies implement Writable so they can be written to the file system. 
- Modified ClusterIterator and CIMapper to write and read the appropriate clustering policy. 

Next steps need to address the fact that clusters do not serialize their observation state (s0, s1, s2) and so the MR version of ClusterIterator does not actually produce correct values. This will be a much bigger project.