A Boolean value that determines whether the button displays its border only when the pointer is over it.
The value of this property is YES if the button’s border is displayed only when the pointer is over the button and the button is active. The value is NO if the border is displayed all the time, regardless of the position of the pointer. By default, this method returns NO.
If bordered is NO, the border is never displayed, regardless of the value of showsBorderOnlyWhileMouseInside.