* Improve a variable name:  entry0 --> table. * Give set_lookkey_string() a fast alternate path when no dummy entries   are present. * Have set_swap_bodies() reset the hash field to -1 whenever either of   bodies is not a frozenset.  Maintains the invariant of regular sets   always having -1 in the hash field; otherwise, any mutation would make   the hash value invalid. * Use an entry pointer to simplify the code in frozenset_hash().
* Improve a variable name:  entry0 --> table.
* Give set_lookkey_string() a fast alternate path when no dummy entries
  are present.
* Have set_swap_bodies() reset the hash field to -1 whenever either of
  bodies is not a frozenset.  Maintains the invariant of regular sets
  always having -1 in the hash field; otherwise, any mutation would make
  the hash value invalid.
* Use an entry pointer to simplify the code in frozenset_hash().

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator