Log Message:
Update kdirstat to 2.4.0.

Changes Overview:
 o Fixed crash when quitting program while directory reading in progress.
 o Fixed crash when trying to open another directory for reading while
   reading still in progress. This is really just a variant of the above
   bug.
 o Added German translation contributed by Christoph Eckert.
 o Added Stop Reading toolbar button (and menu entry) to abort directory
   reading while in progress.