Made mason6.clj a good bit faster

Made mason6 a good bit faster, however, mason 7 and 8 still are a lot faster. Clojure doesn't allow primitive type hinting for functions with greater than 4 arguments, so a lot of performance is lost there. Also, == is usually more performant than = for tight loops.
Couple of other tricks I noticed: adding negative numbers is a little faster than subtracting.
typing ^"[[I" for double int arrays is a bit faster than ^objects, but not much.