The message_timeout field was basically polled. But ever since the OSC
was changed to work more event based, this didn't quite work. It was
quite visible when switching subtitle or audio tracks while paused (and
with caching disabled, since the cache update triggered some extra
redrawing).
Fix by using a proper timer.
I noticed that changing tracks with the message call commented didn't
redraw properly either, but, uh, I guess the message is always triggered
anyway, and happens to take care of this.
cb2b5553bf