WARNING: Standardize button press and release button parameter values. This may break existing code using 3rd mouse button press/release events. The motion callback and OS/2 had been passing the 3rd mouse button as value 4. Other platforms were passing it as value 3. Since button/press and release events only have a single button values 1,2,3 were unique... but OS/2 was passing the mask value instead, making these not work cross platform. I decided to make the button press/release and motion events all function the same. Passing the mask values instead of button numbers. This change will only affect button 3 on button press or release events on Windows, Mac and GTK. OS/2 already functioned this way, iOS and Android do not support button 3.