Dragging slider modifies values, even if callback returns false

Line 347 of ui.slider.js:

                var newValues = this.values();
                newValues[index] = newVal;

actually modifies the value. This causes two problems:

1) One can't determine the old value inside the slide callbacks (for example, to determine if the slider is being dragged to the left or right).

2) Possibly the cause of bug #4385, since the value will be changed, and all further requests will be fail because of this.

Should probably change this to:

                var newValues = this.values().clone();
                newValues[index] = newVal;