box2d: add a box only with a left button.
box2d: add a box only with a left button.

Due to backward compat, the wheel *also* acts as a mouse button press
now and adds quite insane amount of boxes. Do not want.

mosra/magnum-examples,mosra/magnum-examples,mosra/magnum-examples,Squareys/magnum-examples,mosra/magnum-examples,mosra/magnum-examples,mosra/magnum-examples,Squareys/magnum-examples,mosra/magnum-examples,Squareys/magnum-examples,Squareys/magnum-examples