Returns an iterator for values in this priority list.
@method sjl.stdlib.PriorityList#values
@overrides sjl.stdlib.SjlMap#values
@returns {sjl.stdlib.Iterator}
function () {
            if (this.wrapItems) {
                return new Iterator(this.sort()._values.map(function (item) {
                    return item.value;
                }));
            }
            return new SjlMap.prototype.values.call(this.sort());
        }