xfibx: no update of tooltip if window name changes

[Jens Guballa]

Hi Toby,

I think xfibx can be improved:

When the title of a window changes, the tooltip for the corresponding
icon in xfibx should be updated, too (like it is done in the taskbar).

BTW, xfibx is *very* cool!

Viele Grüße
Jens