[xmonad] separate log for each Xinerama screen

[Oleksandr Manzyuk]

Hi Adam,

Thanks for the link to your configuration.  Indeed, it basically
provides the behavior I wanted to have, except that I also wanted to
make the status bar on an unfocused screen show something useful (like
the title of the last focused window and the layout on that screen).
On the other hand, your code allows to use different pretty-printers
for the focused and unfocused screens.

Hm... It looks like the changes I am suggesting are not general
enough.  Should I make a patch or should we think about factoring the
existing functionality even further?  In the former case, should I
change the (admittedly provisional) names dynamicLogWithPP',
dynamicLogString', and pprWindowSet' to longer but more descriptive
dynamicLogWithPPonScreen, dynamicLogStringOnScreen, and
ppWindowSetOnScreen?

Best,
Sasha