Support GL windows on retina display when app does not set Fl::use_high_res_GL(1)

git-svn-id: file:///fltk/svn/fltk/branches/branch-1.4@13078 ea41ed52-d2ee-0310-a9c1-e6b18d33e121

src/Fl_cocoa.mm

@@ -2202,6 +2202,7 @@ static CGContextRef prepare_bitmap_for_layer(int w, int h ) {
 
 @implementation FLViewGL
 - (void)displayLayer:(CALayer *)layer {
+  if (!Fl::use_high_res_GL()) layer.contentsScale = 1.;
   [self drawRect:[self frame]];
   Fl_Window *window = [(FLWindow*)[self window] getFl_Window];
   if (window->parent()) window->redraw(); // useful during resize of GL subwindow