bitArray: tests, less slicing, clampM, shiftLeftM, byteswapM

byteswapM will be useful for some of my other pending pull requests (which I'll rebase if this gets merged)

* not sure whether shift left is actually faster than shift right... but i think it looks more "naturally"
* the closure compiler is crap with closures... it looks like it is working with bitArray, but it regulary kills my prototypes... (bitArray is just a namespace, not a prototype - that might be the reason it is working)