[openbeos] Tracker column resizing fix.

Hey Axel.
You commited a fix for the Tracker column resizing problem but I am not sure what you did was the best option. The change you did just works-around the original problem which is an inordinate number of update messages being sent. I mention this because the same problem happens with BSliders and probably any other component/feature that relies on update messages. 

-Bruno

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