Fix "Mac: Most fl_symbols missing corner pixels" (#1409).

src/drivers/Quartz/Fl_Quartz_Graphics_Driver.H

@@ -98,6 +98,7 @@ protected:
   int not_clipped(int x, int y, int w, int h) FL_OVERRIDE;
   void restore_clip() FL_OVERRIDE;
   void end_points() FL_OVERRIDE;
+  void end_loop() FL_OVERRIDE;
   void end_line() FL_OVERRIDE;
   void end_polygon() FL_OVERRIDE;
   void end_complex_polygon() FL_OVERRIDE;

src/drivers/Quartz/Fl_Quartz_Graphics_Driver_vertex.cxx

@@ -33,6 +33,13 @@ void Fl_Quartz_Graphics_Driver::end_points() {
   }
 }
 
+void Fl_Quartz_Graphics_Driver::end_loop() {
+  CGContextSaveGState(gc_);
+  CGContextSetLineCap(gc_, kCGLineCapSquare);
+  Fl_Graphics_Driver::end_loop();
+  CGContextRestoreGState(gc_);
+}
+
 void Fl_Quartz_Graphics_Driver::end_line() {
   if (n < 2) {
     end_points();