* bpo-30197: Enhance functions swap_attr() and swap_item() in test.support.

They now work when delete replaced attribute or item inside the with
statement.  The old value of the attribute or item (or None if it doesn't
exist) now will be assigned to the target of the "as" clause, if there is
one.

* Update docstrings.

On clang, only compile dtoa.c with -fno-strict-aliasing, use strict
aliasing to compile all other C files.

There were two almost identical definitions of bytes1.

* bpo-30175: Skip client cert tests of test_imaplib

The IMAP server cyrus.andrew.cmu.edu doesn't accept our randomly
generated client x509 certificate anymore.

* bpo-30188: Catch EOFError in NetworkedNNTPTests

test_nntplib fails randomly with EOFError in
NetworkedNNTPTests.setUpClass(). Catch EOFError to skip tests in that
case.

QueueListenerTest of test_logging now closes the multiprocessing
Queue and joins its thread to prevent leaking dangling threads to
following tests.

Add also @support.reap_threads to detect earlier if a test leaks
threads (and try to "cleanup" these threads).

bpo-28769 changed PyUnicode_AsUTF8() return type from const char* to
char* in Python 3.7, but tm_zone field type of the tm structure is
char* on FreeBSD.

Cast PyUnicode_AsUTF8() to char* in gettmarg() to fix the warning:

    Modules/timemodule.c:443:20: warning: assigning to 'char *'
    from 'const char *' discards qualifiers

* Fix PEP 8 (SomeType instead of some_type)
* Add a function parameter annotation
* Explain, using wording from PEP 484 and PEP 526,
  why one annotation is in quotes and another is not.

Suggested by Ivan Levkevskyi.

Builtin container types have two potential link targets in the docs:

- their entry in the list of builtin callables
- their type documentation

This change brings `bytes` and `bytearray` into line with other
container types by having cross-references default to linking to
their type documentation, rather than their builtin callable entry.

On macOS, SuppressCrashReport now redirects /usr/bin/defaults command
stderr into a pipe to not pollute stderr. It fixes a
test_io.test_daemon_threads_shutdown_stderr_deadlock() failure when
the CrashReporter domain doesn't exists. Message logged into stderr:

2017-04-24 16:57:21.432 defaults[41046:2462851]
The domain/default pair of (com.apple.CrashReporter, DialogType) does not exist

Clarify that a sequence of strings is the preferred value for 'field_names'.

test_build_ext() of test_distutils now uses support.temp_cwd() to
prevent the creation of a pdb file in the current working directory
on Windows.

timegm() return type is time_t, not int. Use time_t to prevent the
following compiler warning on Windows:

timemodule.c: warning C4244: '=': conversion from 'time_t' to 'int',
              possible loss of data

* Use @support.reap_threads on unit tests creating threads
* Call TestCase.fail() on thread.join(timeout) failure

At the time when an abstract base class' __init_subclass__ runs,
ABCMeta.__new__ has not yet finished running, so in the presence of
__init_subclass__, inspect.isabstract() can no longer depend only on
TPFLAGS_IS_ABSTRACT.

The constrain was removed in bpo-29816.

The bug was added in still not released version.

Disable faulthandler to run test_SEH() of test_ctypes to prevent the
following log with a traceback:

    Windows fatal exception: access violation

Add support.disable_faulthandler() context manager.

* bpo-30125: Cleanup faulthandler.c

* Use size_t type for iterators
* Add { ... }

* bpo-30125: Fix faulthandler.disable() on Windows

On Windows, faulthandler.disable() now removes the exception handler
installed by faulthandler.enable().

test_io has two unit tests which trigger a deadlock:

* test_daemon_threads_shutdown_stdout_deadlock()
* test_daemon_threads_shutdown_stderr_deadlock()

These tests call Py_FatalError() if the expected bug is triggered
which calls abort(). Use test.support.SuppressCrashReport to prevent
the creation on a core dump, to fix the warning:

Warning -- files was modified by test_io
  Before: []
  After:  ['python.core']

test_quick_connect() runs a thread up to 50 seconds, whereas the
socket is connected in 0.2 second and then the thread is expected to
end in less than 3 second. On Linux, the thread ends quickly because
select() seems to always return quickly. On FreeBSD, sometimes
select() fails with timeout and so the thread runs much longer than
expected.

Fix the thread timeout to fix a race condition in the test.

Detect when the "cc" compiler (and the $CC variable) is the Clang
compiler. The test is needed to add the -fno-strict-aliasing option
on FreeBSD where cc is clang.