Vector3.js - Optimizations

Vector3.js Optimization …
- variable reuse (less mem, faster attribution - http://jsperf.com/pro-var-reuse);
- faster <Vector3>.crossVectors() (http://jsperf.com/three-js-vector3-crossvectors-opt);
- "undefined" replaced by "void(0)", since is slight faster, value safe and uses less chars (http://jsperf.com/typeof-vs-undefined-check/21);
- <Vector3>.angleTo() uses one less variable;
- faster <Vector3>.roundToZero(), using bitwise operator;
- faster <Vector3>.divideScalar();
- using *-1 to negate Vector3 properties (better minification, http://jsperf.com/fast-negate-numeric-property).