[STUMP] multihead frame number bug

[John Li]

There is a bug in stumpwm's handling of frame numbering in hotplugged
multihead setups. I can reproduce it with these steps:

1. Start stumpwm on my laptop and split the screen in half so I get
frames 0 and 1.
2. Plug in an external LCD. Run "xrandr --output VGA --auto" and
"xrandr --output VGA --pos 1280x0" to position the external monitor to
the right of the laptop screen.

Now, frames 0 and 1 will shift over to the external monitor and
another frame will appear on the laptop screen, numbered 1. Creating
new frames on the laptop screen results in frames that are _all_
numbered 2.

I'm using the latest git version and I'm getting the frame numbers
by calling fselect.

Calling the only function on both screens fixes the problem, as far as
I can tell.


-John