fix gtk canvas reset

collects/mred/private/wx/gtk/canvas.rkt

@@ -204,12 +204,12 @@
       (gtk_widget_queue_draw client-gtk))
     
     (define/public (reset-child-dcs)
-      (send dc reset-dc #t))
+      (send dc reset-dc))
     (define/override (maybe-register-as-child parent on?)
       (register-as-child parent on?))
 
     (define/override (internal-on-client-size w h)
-      (send dc reset-dc #f))
+      (send dc reset-dc))
     (define/override (on-client-size w h) 
       (let ([xb (box 0)]
             [yb (box 0)])

collects/mred/private/wx/gtk/dc.rkt

@@ -31,15 +31,13 @@
                  (set! c (gdk_cairo_create w))
                  c))))
 
-    (define/public (reset-dc force?)
-      (when (or force?
-                (eq? 'windows (system-type)))
+    (define/public (reset-dc)
       ;; FIXME: ensure that the dc is not in use
       (as-entry
        (lambda ()
          (when c
            (cairo_destroy c)
-	     (set! c #f))))))
+           (set! c #f)))))
 
     (define/override (get-size)
       (let-values ([(w h) (get-client-size)])