Allow building the _uuid extension module on FreeBSD and OpenBSD.

- primary change is to add a new default filter entry for
  'default::DeprecationWarning:__main__'
- secondary change is an internal one to cope with plain
  strings in the warning module's internal filter list
  (this avoids the need to create a compiled regex object
  early on during interpreter startup)
- assorted documentation updates, including many more
  examples of configuring the warnings settings
- additional tests to ensure that both the pure Python and
  the C accelerated warnings modules have the expected
  default configuration

Third party projects may wish to hide their own internal machinery in
order to present more comprehensible tracebacks to end users
(e.g. Jinja2 and Trio both do this).

Previously such projects have had to rely on ctypes to do so:

  https://github.com/pallets/jinja/blob/fe3dadacdf4cf411d0a5b6bbd4d5234697a28af2/jinja2/debug.py#L345
  https://github.com/python-trio/trio/blob/1e86b1aee8c0c759f6f239ae53a05d0d3963c629/trio/_core/_multierror.py#L296

This provides a Python level API for creating and modifying real
Traceback objects, allowing tracebacks to be edited at runtime.

Patch by Nathaniel Smith.

It's more trouble than it's worth, since AppVeyor only checks the HEAD commit of a PR rather than the full diff against the base branch to decide which files changed.

bpo-32499: Add dataclasses.is_dataclass(obj), which returns True if obj is a dataclass or an instance of one. (#5113) 

The picklers do no longer allocate temporary memory when dumping large
bytes and str objects into a file object. Instead the data is
directly streamed into the underlying file object.

Previously the C implementation would buffer all content and issue a
single call to file.write() at the end of the dump. With protocol 4
this behavior has changed to issue one call to file.write() per frame.

The Python pickler with protocol 4 now dumps each frame content as a
memoryview to an IOBytes instance that is never reused and the
memoryview is no longer released after the call to write. This makes it
possible for the file object to delay access to the memoryview of
previous frames without forcing any additional memory copy as was
already possible with the C pickler.

Add a new argument "-m" to the pdb module to allow
users to run `python -m pdb -m my_module_name`.

This relies on private APIs in the runpy module to work,
but we can get away with that since they're both part of
the standard library and can be updated together if
the runpy internals get refactored.

This module has never been enabled by default, never worked correctly
on x86-64, and caused ABI problems that caused C extension
compatibility. See bpo-29137 for details/discussion.

Fix deadlocks in :class:`concurrent.futures.ProcessPoolExecutor` when task arguments or results cause pickling or unpickling errors.
This should make sure that calls to the :class:`ProcessPoolExecutor` API always eventually return.

Overriding flags to 0 will make the default pattern matching only
lower case letters.

The comment was added in 3abca127.
In d78448e9, it was changed to
use PyArg_ParseTuple instead.

Addition and subtraction of arbitrary numbers no longer allowed.

Otherwise the import team gets flagged for reviews any time the bytecode for
importlib.h changes (e.g new bytecode, optimizations, etc.).

Updates documentation for generator expressions in classes tutorial: Clarify usage of ambiguous term "brackets" by replacing with "square brackets". Updated subsequent lines to respect line breaks. (#5079)

Move other test to more proper place.

bpo-32468: Better frame repr()