Fix focus follow mouse usability problem

[Simon Thum]

Harald Braumann wrote:
> If it's not possible yet, are there plans to implement such
> functionality in the X server? Like sending an event whenever the
> pointer stops?
Well, X is in pretty much the same situation here; it just knows when
the mouse moves, or when it did so last time (plus something else happens).

There is a distinct advantage the server has, namely, it knows more
detail. So it could do a better job than a client/wm. But still that's
far from perfect, which I guess is why reading tea leaves has been left
to the client.

A possible alternative could be to synthesize inferred proximity from
the driver and make $WM use that. This however doesn't exactly solve the
problem, is hard to do (especially above the driver), so I guess devs
will hate it.