* src/uimacnew09/ProgressCell.m: Return to retaining and releasing the
  icon and status string.  This was causing crashes if opening a group
  while syncing, because the status could be updated while the outline
  was in progress of drawing, so that the string reference was invalid
  by the time it rendered.  Added copyWithZone to resolve the original
  bugs reported by Onne Gorter. Discussion on why copyWithZone is
  required for NSCell is at
  https://mikeash.com/pyblog/friday-qa-2010-08-27-defensive-programming-in-cocoa.html