ATTR_DIMMED for SetTreeItemAtribute()

[vix]

A tree control can be used to implement radio button controls;

in this situation you can't completely dim one of the items (so that it is grayed and the user immediately sees it is inactive) because the function SetTreeItemAttribute() doesn't allow ATTR_DIMMED attribute.

You can dim the item label using SetTreeCellAttribute(), but the check box stays active (see this discussion).

The EVENT_MARK_STATE_CHANGE can be swallowed, but the check box has the aspect of an active check box, even if nothing happens when you click over it.

I suggest to add the attribute ATTR_DIMMED to SetTreeItemAttribute() so that the whole item can be dimmed (its check box too)