Updated event registration for touch devices.

Hello kangax, I've experienced problems with an IPad4 and object movement on the canvas.

I do not know if this is a wanted behaviour, but when an object is moved on the canvas, we receive not only touch events but mouse events too. 

Initially the event handling is added for touch events only, but when the first event comes in the mouse event listener is added too.

This caused a rect to move to a completely other direction, when we just tab the device once. 
  
Best Regards