winemac: Tell Cocoa that we don't draw a focus ring for our views.

This seems to eliminate a lot of house-keeping work inside Cocoa.

dlls/winemac.drv/cocoa_window.m

@@ -358,6 +358,11 @@ - (void) completeText:(NSString*)text
         [[self inputContext] discardMarkedText];
     }
 
+    - (NSFocusRingType) focusRingType
+    {
+        return NSFocusRingTypeNone;
+    }
+
     /*
      * ---------- NSTextInputClient methods ----------
      */