nct type in 2.3, builtin names True and False were also added to
      2.2.2, mapping to ints 1 and 0.  For compatibility in both directions,
      True gets pickled as INT + "I01\n", and False as INT + "I00\n".
      Leading zeroes are never produced for a genuine integer.  The 2.3
      (and later) unpicklers special-case these and return bool instead;
      earlier unpicklers ignore the leading "0" and return the int.
      rī