[Xmonad] darcs patch: use a global IORef to keep list of urgent windows

[Don Stewart]

allbery:
> 
> On Oct 30, 2007, at 11:25 , Don Stewart wrote:
> 
> >Oh, that's an issue -- now you've hidden state away in a module,  
> >how are
> >we going to get at it to serialise? This is why global state is bad.
> 
> Urgency hints are ephemeral state, for which the window manager is  
> *not* authoritative; you do not want to save it, you want to  
> reconstruct it on restart by checking extant windows' urgency hints.

Yes, which opens up the issue of how you initialise state on 
restart with extensions, as they don't provide setup or teardown
methods.

So while for this particular case, local iorefs will work, its
not a scalable solution to extensions needing state.

-- Don