Correctness fixes to match Okasaki and Gill's paper, but the union function is still not working correctly.
More IntMap tests.
Temporarily modified the BitOps used for IntMap and IntSet so they implement little-endian operations instead of big-endian operations; this is just to make sure the implementation of the map/set operations themselves are robust.
Fixed some issues with IntMap.Union, though it still doesn't work 100% correctly.
Fixed the IntMap.Union function so it works correctly.