SceneJS_math_addVec4 = function(u, v, dest) {
    if (!dest) {
        dest = u;
    }

    dest[0] = u[0] + v[0];
    dest[1] = u[1] + v[1];
    dest[2] = u[2] + v[2];
    dest[3] = u[3] + v[3];

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