valueDiff for arrays?

[Alex Tweedly]

Earlier, Alex Tweedly said some nonsense like:

> arrays are hashed - even if quickly, while byte chunks are constant time.
>
> So replace both uses of the array np with a byte chunk.
> ...
>
> Takes about 40% off the time.
>
> -- Alex.
Operator error !
Forget what I said, it was wrong.

I'll do the test more carefully and send a report later (whether it 
speeds the test up or not).

Alex