[wmii] wmii-2.5 segfault.

Hello,

I occasionnaly get a segfault when running wmii-2.5, compiled from the
mercurial repository (changeset 39), running on an iBook G4 with
Debian. Backtrace attached. IIRC it happened on a workspace with
firefox running, while pressing Ctrl-U to see page source, but I'm no
too sure. I can give more information if needed.

Hope this helps, and thanks for the great software!