[xmonad] Pointer follows focus (with patch)

[Don Stewart]

xmonad:
> Thanks Robert! I got your code to work in my Config.hs
> without any modifications to xmonad. Here's what I have:
> 
> pointerFollowsFocus ::  Rational -> Rational -> X ()
> pointerFollowsFocus h v = do
>     dpy <- asks display
>     root <- asks theRoot
>     withFocused $ \w -> do
>         wa <- io $ getWindowAttributes dpy w
>         (sameRoot,_,w',_,_,_,_,_) <- io $ queryPointer dpy root
>         if (sameRoot && w == w') then
>             return ()
>            else
>             io $ warpPointer dpy none w 0 0 0 0
>                 (fraction h (wa_width wa)) (fraction v (wa_height wa))
>           where fraction x y = floor (x * fromIntegral y)
> [...]
> logHook = dynamicLogWithPP hethraelPP
>     {ppOutput = hPutStrLn xmobar } >> pointerFollowsFocus 1 1
> 
> 'unless' was not in scope, so I changed it to an if
> statement.
> 
> I have found a couple of issues with it, but otherwise it's
> great. First, the pointer warps when tabs are clicked. The
> second is a little more complicated. When using a full or
> tabbed layout, calling focusDown (mod+J) to move from the
> last window to the first window causes the pointer to warp
> even if the pointer is in the window. When calling focusUp
> (mod+K), the pointer always warps unless moving from the
> master window to the last window.

Once this is finalised, can we get it as an extension module
for mouse/pointer stuff. Saves people reimplementing this functionality