* bpo-22490: Remove "__PYVENV_LAUNCHER__" from the shell environment on macOS

This changeset removes the environment varialbe "__PYVENV_LAUNCHER__"
during interpreter launch as it is only needed to communicate between
the stub executable in framework installs and the actual interpreter.

Leaving the environment variable present may lead to misbehaviour when
launching other scripts.

* Actually commit the changes for issue 22490...

* Correct typo

Co-Authored-By: Nicola Soranzo <nicola.soranzo@gmail.com>

* Run make patchcheck

Co-authored-by: Jason R. Coombs <jaraco@jaraco.com>
Co-authored-by: Nicola Soranzo <nicola.soranzo@gmail.com>

Plistlib currently throws an exception when asked to decode a valid
.plist file that was generated by Apple's NSKeyedArchiver. Specifically,
this is caused by a byte 0x80 (signifying a UID) not being understood.

This fixes the problem by enabling the binary plist reader and writer
to read and write plistlib.UID objects.

Values in the range of an unsigned long long, but outside of the range
of a signed long long were serialized as a negative value.

Due to a bug in PyObjC my test scripts indicated that the previous behavior
matched Apple's plist code, instead the handle large unsigned values correctly.

The change to plistlib.py is from a patch by Serhiy.

requires them.  Disable executable bits and shebang lines in test and
benchmark files in order to prevent using a random system python, and in
source files of modules which don't provide command line interface.  Fixed
shebang lines in the unittestgui and checkpip scripts.

requires them.  Disable executable bits and shebang lines in test and
benchmark files in order to prevent using a random system python, and in
source files of modules which don't provide command line interface.  Fixed
shebang line to use python3 executable in the unittestgui script.

* Negative integer support in binary plists was broken

* Better exception for invalid data

* Fix the versionadded/versionchanged markup in the documentation

* Add the interface cleanup to what's new for 3.4

This patch adds support for binary plists on OSX to plistlib (based
on a patch by 'dpounces').

The patch also cleans up the API for the plistlib module.