* bpo-33972: Fix EmailMessage.iter_attachments raising AttributeError.

When certain malformed messages have content-type set to 'mulitpart/*' but
still have a single part body, iter_attachments can raise AttributeError. This
patch fixes it by returning a None value instead when the body is single part.

Use os.getgroups() rather than grp.getgrall() to get groups.
Rename also the test to test_chown_gid().

Python now gets the absolute path of the script filename specified on
the command line (ex: "python3 script.py"): the __file__ attribute of
the __main__ module, sys.argv[0] and sys.path[0] become an absolute
path, rather than a relative path.

* Add _Py_isabs() and _Py_abspath() functions.
* _PyConfig_Read() now tries to get the absolute path of
  run_filename, but keeps the relative path if _Py_abspath() fails.
* Reimplement os._getfullpathname() using _Py_abspath().
* Use _Py_isabs() in getpath.c.

test.pythoninfo now also logs pwd.getpwuid(os.getuid()) and
os.getgrouplist(). Extract also os.getrandom() test to run it first.

* The UTF-8 incremental decoders fails now fast if encounter
  a sequence that can't be handled by the error handler.
* The UTF-16 incremental decoders with the surrogatepass error
  handler decodes now a lone low surrogate with final=False.

eval() was being called an extra time without a filter for
deprecation warnings.

Remove sys.getcheckinterval() and sys.setcheckinterval() functions.
They were deprecated since Python 3.2. Use sys.getswitchinterval()
and sys.setswitchinterval() instead.

Remove also check_interval field of the PyInterpreterState structure.

* regrtest: Add --cleanup option to remove "test_python_*" directories
  of previous failed test jobs.
* Add "make cleantest" to run "python3 -m test --cleanup".

At the moment you can definitely use UDPLITE sockets on Linux systems, but it would be good if this support were formalized such that you can detect support at runtime easily.

At the moment, to make and use a UDPLITE socket requires something like the following code:

```
>>> import socket
>>> a = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, 136)
>>> b = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, 136)
>>> a.bind(('localhost', 44444))
>>> b.sendto(b'test'*256, ('localhost', 44444))
>>> b.setsockopt(136, 10, 16)
>>> b.sendto(b'test'*256, ('localhost', 44444))
>>> b.setsockopt(136, 10, 32)
>>> b.sendto(b'test'*256, ('localhost', 44444))
>>> b.setsockopt(136, 10, 64)
>>> b.sendto(b'test'*256, ('localhost', 44444))
```

If you look at this through Wireshark, you can see that the packets are different in that the checksums and checksum coverages change.

With the pull request that I am submitting momentarily, you could do the following code instead:

```
>>> import socket
>>> a = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDPLITE)
>>> b = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDPLITE)
>>> a.bind(('localhost', 44444))
>>> b.sendto(b'test'*256, ('localhost', 44444))
>>> b.set_send_checksum_coverage(16)
>>> b.sendto(b'test'*256, ('localhost', 44444))
>>> b.set_send_checksum_coverage(32)
>>> b.sendto(b'test'*256, ('localhost', 44444))
>>> b.set_send_checksum_coverage(64)
>>> b.sendto(b'test'*256, ('localhost', 44444))
```

One can also detect support for UDPLITE just by checking

```
>>> hasattr(socket, 'IPPROTO_UDPLITE')
```


https://bugs.python.org/issue37345

`_PyUnicode_Writer` is a relatively complex structure.  Initializing it is significant overhead when decoding short ASCII string.

When the Windows default event loop changed, `asyncio-policy.rst` was updated but `asyncio-eventloop.rst` was missed.

… as proposed in PEP 572; key is now evaluated before value.





https://bugs.python.org/issue35224

Rephrase and clarify that "the entire Python program exits when only daemon threads are left". This matches the documentation at https://docs.python.org/3/library/threading.html#thread-objects.

When the test is ran with `PYTHONWARNINGS=error` the environment variable is passed to the python interpreter used in `assert_python_ok` where `DeprecationWarning` from  `@asyncio.coroutine` is converted into an error. Ignore the `DeprecationWarning` in `assert_python_ok`.


https://bugs.python.org/issue37323

https://bugs.python.org/issue37364

test_gdb no longer fails if it gets an "unexpected" message on
stderr: it now ignores stderr. The purpose of test_gdb is to test
that python-gdb.py commands work as expected, not to test gdb.

This is to help prevent people from accidentally installing into the wrong Python interpreter if they are not aware of which Python interpreter `pip` points to.

Also, add a missing call to va_end() in PySys_Audit().

* Switch to officially supported curses from 3rd-party ASIS supported ncurses
* stop saying optional modules osaudiodev and spwd are missing on AIX

Patch by M.Felt

* Docs: Improved phrasing 

Removed usage of second person pronouns in the section and made the assumption of "uneasiness" in code style transition more neutral.

* Removed trailing whitespace on line 34