Bug1676: correct repaint of rearranged tracks on Linux...

... This little one-line fix is the right thing to do.  I do not understand
deeply enough how Linux repainting events are sequenced differently from
Windows or Mac, but I understand the code history enough to know where the
bug was introduced.

Problem was that full Refresh of TrackPanel used to be done earlier, in our
handlers of custom events emitted by TrackList; but now that handling is
delayed, for good reasons, so it is correct that the UIHandle object
should request the early full refresh explicitly, not relying on TrackList
event handling.

See explanations here http://bugzilla.audacityteam.org/show_bug.cgi?id=1676#c6

src/tracks/ui/TrackSelectHandle.cpp

@@ -146,7 +146,7 @@ UIHandle::Result TrackSelectHandle::Drag
    // track is fully on-screen.
    CalculateRearrangingThresholds(event);
 
-   result |= EnsureVisible;
+   result |= EnsureVisible | RefreshAll;
    return result;
 }