Thu May 17 00:55:09 BST 2012 Brian Warner <warner@lothar.com>

Thu May 17 00:55:09 BST 2012  Brian Warner <warner@lothar.com>
  * dictutil.DictOfSets: remove .union() method, it was misleading

  Unlike set.union(), which returns a new set, DictOfSets.union() modified
  the DictOfSets in-place. The name collision bit me when I changed some
  code from using DictOfSets to a normal set, and expected that
  set.union() would modify the set in-place. Since there was only one user
  of DictOfSets.union, I figured it was safer to just get rid of it.