computation as the overflow behavior of signed integers is undefined.

In practice we require compiling everything with -fwrapv which forces overflow
to be defined as twos compliment but this keeps the code cleaner for checkers
or in the case where someone has compiled it without -fwrapv or their
compiler's equivalent.

Found by Clang trunk's Undefined Behavior Sanitizer (UBSan).

Cleanup only - no functionality or hash values change.

Found by Clang trunk's Undefined-Behavior Sanitizer.  [more to come]

Turns out, the snakebite bots behave also their peculiarities.

I'm really not proud of this stream of commits. :(

The Windows buildbots seem to be unable to agree whether they need them or not.

It cause shutil.rmtree not ignore all errors. Also add a test ensuring that
rmtree fails when being called on a symlink. Patch by Serhiy Storchaka.

This commit updates a test broken by the change made for issue #14783.

Issue #16248: Disable code execution from the user's home directory by tkinter when the -E flag is passed to Python.
Patch by Zachary Ware.

Issue #16248: Disable code execution from the user's home directory by tkinter when the -E flag is passed to Python.
Patch by Zachary Ware.

Original patch by Julien Courteau and Pierre Paul Lefebvre.

Issue #16602: When a weakref's target was part of a long deallocation chain, the object could remain reachable through its weakref even though its refcount had dropped to zero.

Thanks to Eugene Toder for diagnosing and reporting the issue.

There was a window between the write and the chmod where the user’s
password would be exposed, depending on default permissions.  Philip
Jenvey’s patch fixes it.

These files are created by some NFS clients a file is edited and removed
concurrently (see added link in doc for more info).  If such a file is
removed between distutils calls listdir and copy, it will get confused.
Other special files are ignored in sdist (namely VCS directories), but
this has to be filtered out earlier.

Patch by Steven Kryskalla.

Patch by Ilya Sandler.

encoded/decoded to/from UTF-8/surrogateescape, instead of the locale encoding
(which may be ASCII if no locale environment variable is set), to avoid
inconsistencies with os.fsencode() and os.fsdecode() functions which are
already using UTF-8/surrogateescape.

Patch by Serhiy Storchaka.

Patch by Jonathan Kotta.

Patch by Serhiy Storchaka.

#16549: Make json.tool work again on Python 3 and add tests.  Initial patch by Berker Peksag and Serhiy Storchaka.