mouse joint problem on mobile devices

[codinglava]

If we use box2d on a mobile device:

1. mouse_down may occur with no mouse_move before it
2. if we use mouse joint then for some reason "createDragJoint" is always called before a mouse_down in Input class
3. so then Input.mousePos contains invalid coord when createDragJoint called

Calling Input.initialize before World.create won't help.

Workaround is to listen for Input's mouse_down in capture phase
(Input.as, line 49:
s.addEventListener(MouseEvent.MOUSE_DOWN, handleMouseDown, true, 0, true);
)

Not sure if this a good way to fix it..