Lots of changes for the April 1, 2014 edition:
Added Vinnie Falco as co-author.  He has contributed much, including much better names than I had, the universal aspect of 'uhash', and invaluable testing.
Introduced the type trait: is_contiguously_hashable.  This is a huge optimization.
Changed the type of X to have more realistic values (restricted to realistic ranges instead of being completely random).  This stresses the hash functions more in the quality department.