make the tooltips for the drracket toolbar buttons go away when they

get any events (this shouldn't be necessary unless one gets lost
somehow, but apparently that can happen)

original commit: 3b2cf3f7a4bc4949fc5fa3f626f789ff983be64a

collects/mrlib/switchable-button.rkt

@@ -39,10 +39,13 @@
           (send dc set-pen pen)
           (send dc set-brush brush)
           (send dc set-font font))))
+    
+    (define/override (on-event evt)
+      (show #f))
         
     (inherit stretchable-width stretchable-height
              min-width min-height
-             get-client-size get-dc)
+             get-client-size get-dc show)
     (super-new)
     (let-values ([(tw th _1 _2) (send (get-dc) get-text-extent label small-control-font)])
       (min-width (floor (inexact->exact (+ tw 4))))