Follow upstream VTK.
  520ba015c0b7a451242d0712bd60fd953aa9dfcf
    (Add copy ctors and operators to clear warnings) - but actually, removed;
  1a0b4e9dde815f84e48ee9912d19be9687c97399
    (Refactored how pieces and extents are handled.);
  747b780a9678e397e7d29b5ef90f4edd37a6ba49
    (Updated filters and sources to work with new pipeline logic.) - not removing ivar MaximumNumberOfPieces because it is used in other places than controlling pipeline logic;
  ac6f1854355ca5e141005858ac988bdb73c9039e
    (Moved key.).