So I originally modified `OpenHashMap` only to realize that I really just needed `PrimaryKeyOpenHashMap`.  Both `keySet` and `_values` were previously `protected var` I made them public so that I can use the OpenHashMap to collect unique keys and merge attributes and then split it apart into its separate KeySet and Values tables to be passed along  as separate Index and Values RDDs.  I the reuse the KeySet for temporary aggregators.