function setVec (vec, x, y, z) {
    var propagate = false;

    propagate = _vecOptionalSet(vec, 0, x) || propagate;
    propagate = _vecOptionalSet(vec, 1, y) || propagate;
    propagate = _vecOptionalSet(vec, 2, z) || propagate;

    return propagate;
}
Private method which sets three values within an array of three
using _vecOptionalSet. Returns whether anything has changed.

@method

@param {Array} vec The array to set the values of
@param {Any} x The first value to set within the array
@param {Any} y The second value to set within the array
@param {Any} z The third value to set within the array

@return {Boolean} whether anything has changed