Add a fast_container member to Picklerobject.  If fast is true, then
fast_container counts the depth of nested container calls.  If the
depth exceeds FAST_LIMIT (2000), the fast flag is ignored and the
normal checks occur.  This approach is much like the approach for
prevent stack overflow for comparison and reprs of recursive objects
(e.g. [[...]]).

    - Fast container used for save_list(), save_dict(), and
      save_inst().

      XXX Not clear which other save_xxx() functions should use it.

Make Picklerobject into new-style types, using PyObject_GenericGetAttr()
and PyObject_GenericSetAttr().

    - Use PyMemberDef for binary and fast members

    - Use PyGetSetDef for persistent_id, inst_persistent_id, memo, and
      PicklingError.

      XXX Not all of these seem like they need to use getset, but it's
      not clear why the old getattr() and setattr() had such odd
      semantics.  One change is that the getvalue() attribute will
      exist on all Picklers, not just list-based picklers; I think
      this is a more rationale interface.

There is a long laundry list of other changes:

    - Remove unused #defines for PyList_SET_ITEM() etc.

    - Make some of the indentation consistent

    - Replace uses of cPickle_PyMapping_HasKey() where the first
      argument is self->memo with calls to PyDict_GetItem(), because
      self->memo must be a dictionary.

    - Don't bother to check if cPickle_PyMapping_HasKey() returns < 0,
      because it can only return 0 or 1.

    - Replace uses of PyObject_CallObject() with PyObject_Call(), when
      we can guarantee that the argument tuple is really a tuple.

Performance impacts of these changes:

    - 5% speedup for normal pickling

    - No change to fast-mode pickling.

XXX Really need tests for all the features in cPickle that aren't in
pickle.