isFocused() does not appear to be working for slider

Basically it seems that the isFocused function in a slider always returns false. I assume this is a bug rather than a feature that is not yet working.

Focussing is indeed broken. I haven't really decided yet how the focussing system should work correctly.
So focussing will only work correctly with simple widgets like buttons, checkboxes and edit boxes. Although even the Black style does not load the focus images by default so it basically only works with edit and text boxes out of the box.