Cocoa: avoid screen sync for GC-blit GL context

Affects 10.11 and up

gui-lib/mred/private/wx/cocoa/canvas.rkt

@@ -966,6 +966,9 @@
                            (tell (tell NSImageView alloc) init))])
               (cond
                [gc-via-gl?
+                (tellv (tell glv openGLContext) setValues:
+                       #:type (_ptr i _long) 0
+                       forParameter: #:type _int NSOpenGLCPSwapInterval)
                 (tellv win setAcceptsMouseMovedEvents: #:type _BOOL #t)
                 (set-ivar! win wxb (->wxb this))
                 (set-ivar! glv wxb (->wxb this))

gui-lib/mred/private/wx/cocoa/dc.rkt

@@ -21,7 +21,8 @@
               do-backing-flush)
  display-bitmap-resolution
  make-screen-bitmap
- make-window-bitmap)
+ make-window-bitmap
+ NSOpenGLCPSwapInterval)
 
 (import-class NSOpenGLContext NSScreen NSGraphicsContext NSWindow)