[TESTS] add a benchmark for integer hashing

[TESTS] add a benchmark for integer hashing

If we want to support netmasks for IP address hashing,
we will need something better than a pure modulus, otherwise
people with even numbers of servers will get surprizes.

Bob Jenkins is known for his works on hashing, and his site
has a lot of very interesting researches and algorithms for
integer hashing. He also points to the work of Thomas Wang
who has similar findings.

The program here tests their algorithms in order to find one
well suited for IP address hashing.