Multisample antialiasing

Hi,

I'd like to add anti-aliasing to my OpenGL FLTK 1.3 window.

I've created the window as follows:
    Visualization_box(int x,int y,int w,int h, const char *l=0)
    : Fl_Gl_Window(x,y,w,h,l) {
        m_zoom = 1.0;
        mode(FL_MULTISAMPLE|FL_DOUBLE|mode());
    }
But this has no effect.

I have also not been able to find how to set the number of multisamples with FLTK.

The equivalent SDL code I'm trying to achieve via FLTK would be:
   SDL_GL_SetAttribute(SDL_GL_MULTISAMPLEBUFFERS, 1);
   SDL_GL_SetAttribute(SDL_GL_MULTISAMPLESAMPLES, 4);
which works fine on my platform (OSX).

Does anyone know how to enable antialiasing with FLTK for OSX?

Thanks,
-Adrian