Add SDL_WINDOW_ALLOW_HIGHDPI to SDL_CreateWindow flags so Retina support works on OSX.

legacy/project/src/sdl2/SDL2Stage.cpp

@@ -1481,6 +1481,8 @@ void CreateMainFrame(FrameCreationCallback inOnFrame, int inWidth, int inHeight,
          SDL_GL_SetAttribute(SDL_GL_MULTISAMPLEBUFFERS, true);
          SDL_GL_SetAttribute(SDL_GL_MULTISAMPLESAMPLES, 2);
       }
+
+      requestWindowFlags |= SDL_WINDOW_ALLOW_HIGHDPI;
    }
    
    #ifdef HX_LINUX

project/src/backend/sdl/SDLWindow.cpp

@@ -25,6 +25,7 @@ namespace lime {
 		if (flags & WINDOW_FLAG_HARDWARE) {
 			
 			sdlFlags |= SDL_WINDOW_OPENGL;
+			sdlFlags |= SDL_WINDOW_ALLOW_HIGHDPI;
 			
 			#if defined (HX_WINDOWS) && defined (NATIVE_TOOLKIT_SDL_ANGLE)
 			SDL_GL_SetAttribute (SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_ES);