Iteratirs chnages
- IteratorPool has a global static method to set the numbers of Iterators
  in each pool
- Iterators now returns their full implemntation type, not only an
  Iterator interface.
IndirectSort improvements
- Add a mergesort RT friendly method where temp arrays are passed on
  explicitly.
- Added a pure in-place sort using the dual-pivot quicksort by
  [Yaroslavskiy 2009]