TR: capi:list-panel & callbacks

Hi list,

a follow-up on the pb I submit before.

I did finally implement the timer trick and it seems not so bad. I set it to
50ms. Each select-extend-retract callback reschedule the timer by calling
mp:schedule-timer-relative-milliseconds. So the timer function finally gets
fired 50ms after the last callback is called. The timer function then update
the dependent pane only once.

Xanalys opinion on that trick is very welcome.

Sebastien.