SceneJS_math_negateVector4 = function(v, dest) {
    if (!dest) {
        dest = v;
    }
    dest[0] = -v[0];
    dest[1] = -v[1];
    dest[2] = -v[2];
    dest[3] = -v[3];

    return dest;
}
@param v vec4
@param dest vec4 - optional destination
@return {vec4} dest if specified, v otherwise
@private