Optimized Array Handling in JRE impl

I optimized some code in the JRE Arrays class. This made JBox2D run x-times faster.
I've been working on imaginary jsurf (https://github.com/IMAGINARY/jsurf) GWT version and Dragome version (https://github.com/fpetrola/jsurf/tree/jssurf) and it's using this kind of ClassCastException control flow.

One of main goals in Dragome is to provide a transparent Java usage, and avoid configurations as much as possible. So it's important to allow any kind of piece of software to be executed with less effort inside Dragome environment. 

May be in future versions we could use some heuristics to detect if code is depending on casts and do an automatic configuration of this feature.