The dummy world is a hack for setting up the blitting context properly, when the actual frame buffer isn't used for any other output then 2d blitting. It might not be needed in current versions, so you can try to leave it out and see if that works too.
What the code does is: Render the left eye's view into a texture, render the right eye's view into another texture, blit the resulting textures into the actual frame buffer. That's the easiest way, because otherwise, you would have to render both views into the frame buffer and that's not really possible without a lot of hassle...if even...