Returns #t if the window is enabled when all of its ancestors are enabled, #f otherwise.
Returns #f if the entire radio box is disabled, #t otherwise.
Returns #f if nth radio button is disabled (independet of disabling the entire radio box), #t otherwse. Radio buttons are numbered from 0. If n is equal to or larger than the number of radio buttons in the radio box, an exn:application:mismatch exception is raised.