Remove unused class
Add tests for combining Sum with CountUniqueValues (this checks that the way that the re-reduce occurs is correct; currently it is not)
Re-running the count is really just a way of doing the 're-reduce' phase we need to add manually.
Add a way to add re-reduces when chaining, so that things like Sum work properly when combined with CountUniqueValues
Merge branch 'custommapreduce'