A new murmur3 hashcode implementation contributed by rex kerr. I'm really happy with it. There is benchmarking code included but you can use the pudding for proof: the compiler compiling itself is clearly faster. I deleted the existing murmur2 implementation which has never left trunk in a release. There remain some possible points of improvement with inlining and/or synthetic method generation, but this is a major improvement over the status quo. Closes #2537, review by prokopec.