button-up? in mouse-event%

Returns #t if the event is for a button release, #f otherwise. (As noted in Mouse and Keyboard Events, button release events are sometimes dropped.)

• (send a-mouse-event button-up? button) -> boolean
     button = 'any : symbol in '(left middle right any)

  If button is not 'any, then #t is only returned if it is a release event for a specific button.