[Xmonad] darcs patch: keep focus stack.

[Donald Bruce Stewart]

droundy:
> Hi all,
> 
> Here's a cut at a focus stack.  It's a bit crude, but seems to work.  I had
> to tweak the rotate properties, since rotating the focus (obviously)
> changes the focus stack.  I don't think this weakening of those checks is
> really a Bad Thing.  And I'm a little puzzled how prop_delete_push ever
> passed.  Maybe it failed, and noone noticed? Or maybe we aren't running
> enough tests with large enough stack sizes, so we never ran into the case
> where the focus wasn't on the master window to start with? I don't know,
> but it suggests something is wrong.

Ah ha. The generator wasn't changed when focus was separate from the
stack ordering, so *yes* we only generate StackSets with focus on the
master window. The 'fromList' code for StackSet needs changing.

Good work!

-- Don