[PATCH weston] compositor: add a mouse motion binding type

[Bill Spitzak]

Giulio Camuffo wrote:
> when a mouse is moved the binding handler is called, passing it the
> mouse position and the timestamp. a shell plugin can use this to
> activate an effect when the mouse hits an output corner.

Any preview of resize must be after the client tells the compositor that 
it will not use the mouse for some other purpose at that point.

If the compositor is able to force certain positions to be resize then 
either the "resize edges" are unattractively thick, or that it is very 
hard to grab the resize, or the preview of resize is inconsistent 
because the client has to do it for any internal parts that resize.