* [3.5] bpo-32072: Fix issues with binary plists. (GH-4455)

* Fixed saving bytearrays.
* Identical objects will be saved only once.
* Equal references will be load as identical objects.
* Added support for saving and loading recursive data structures.
(cherry picked from commit a897aee)

* Fix implementation dependent assertion in test_plistlib. (#4813)

It is failed with an advanced optimizer.

Directory and zipfile execution previously added
the parent directory of the directory or zipfile
as sys.path[0] and then subsequently overwrote
it with the directory or zipfile itself.

This caused problems in isolated mode, as it
overwrote the "stdlib as a zip archive" entry
in sys.path, as the parent directory was
never added.

The attempted fix to that issue in bpo-29319
created the opposite problem in *non*-isolated
mode, by potentially leaving the parent
directory on sys.path instead of overwriting it.

This change fixes the root cause of the problem
by removing the whole "add-and-overwrite" dance
for sys.path[0], and instead simply never adds
the parent directory to sys.path in the first
place.

(cherry picked from commit d2977a3ae2cc6802921b1e3b6e9d13fcfbda872d)