bug#16647: Imprecisions with window-resizing cursors

[martin rudalics]

> I'm getting (9 . 0) from both snippets (9 being the frame-char-width). I haven't 
"read" them yet, maybe I'll find something reproducible.
>
> I'm also getting the same results on openbox as I did on xmonad.

I'm beginning to suspect that something strange is going on somewhere
between Emacs and the input device.  Could you try playing a bit with
`mouse-autoselect-window'?  More precisely, how soon (in pixels) it
selects a window when you move the mouse into it from another one.

martin