* Replace testInheritFlags() with two tests:
  testInheritFlagsBlocking() and testInheritFlagsTimeout()
  to test different default socket timeout. Moreover, the test now
  checks sock.gettimeout() rather than a functional test on recv().
* Replace time.time() with time.monotonic()
* Add socket_setdefaulttimeout() context manager to restore the
  default timeout when the test completes.
* Remove testConnect(): accept() wasn't blocking and testAccept()
  already tests non-blocking accept().
* Remove accept() functional test from testInitNonBlocking():
  already tested by testAccept()
* Rewrite testSetBlocking() with a new assert_sock_timeout() method
* Use addCleanup() and context manager to close sockets
* Replace assertTrue(x < y) with assertLess(x, y)

testAccept() and testRecv() of test_socket.NonBlockingTCPTests have a
race condition: time.sleep() is used as a weak synchronization
primitive and the tests fail randomly on slow buildbots.

Use a reliable threading.Event to fix these tests.

Other changes:

* Replace send() with sendall()
* Expect specific BlockingIOError rather than generic OSError
* Add a timeout to select() in testAccept() and testRecv()
* Use addCleanup() to close sockets
* Use assertRaises()

Fix PYTHONCOERCECLOCALE=1 environment variable: only coerce the C
locale if the LC_CTYPE locale is "C".

PyType_GetFlags() return type is unsigned long, not long.

Remove platform.popen() function, it was deprecated since Python 3.3:
use os.popen() instead.

Rename also the "Removed" section to "API and Feature Removals"
of What's New in Python 3.8.

platform._dist_try_harder() was an helper function
for platform.linux_distribution() which has been removed by the
commit 8b94b41a.

test_eintr no longer fails if the signal handler has not been called.

The "busy loops" of test_process_time() and test_thread_time() are
not reliable and fail randomly on Windows: remove them.

This reverts commit 1005c845.

PyStructSequence_GET_ITEM() must be used instead of
PyTuple_GET_ITEM() on a StructTimeType.

Move tupleobject.h code surrounded by "#ifndef Py_LIMITED_API"
to a new Include/cpython/tupleobject.h header file.

Add cpython/ header files to Makefile.pre.in and pythoncore project
of PCbuild.

Fix memory leak in PyUnicode_EncodeLocale() and
PyUnicode_EncodeFSDefault() on error handling.

Changes:

* Fix unicode_encode_locale() error handling
* Fix test_codecs.LocaleCodecTest

Create a new "doctest" job in Travis CI to run "make doctest".

Fix WithThreadsTestPool.test_wrapped_exception()
of test_multiprocessing_fork: join the pool.

WithThreadsTestPool.test_del_pool() is now also decorated
with @support.reap_threads.

Fix the following clang warning:

    Include/cpython/pystate.h:217:3: warning: redefinition of
    typedef 'PyThreadState' is a C11 feature [-Wtypedef-redefinition]

Fix warnings with gcc 8 for wrapperfunc <-> wrapperfunc_kwds casts.

Fix also return type for few other functions (clear, releasebuffer).

Partically revert commit c2e1607a to
fix a reference leak.

"make tags" and "make TAGS" now also parse Include/cpython/ header
files.

'data' argument of unicode_fill() is modified, so it must not be
constant.

Add more assertions to unicode_fill(): check the maximum character
value.

Fix mktime() overflow error in test_email: run
test_localtime_daylight_true_dst_true() and
test_localtime_daylight_false_dst_true() with a specific timezone.

Fix invalid function cast warnings with gcc 8
for method conventions different from METH_NOARGS, METH_O and
METH_VARARGS excluding Argument Clinic generated code.

Fix invalid function cast warnings with gcc 8
for method conventions different from METH_NOARGS, METH_O and
METH_VARARGS in Argument Clinic generated code.

The lineno and col_offset attributes of AST nodes for list comprehensions,
generator expressions and tuples are now point to the opening parenthesis or
square brace. For tuples without parenthesis they point to the position
of the first item.

test_reduce_ex() in test_array.py and
test_reversevaluesiterator_pickling() in test_dict.py weren't using
the highest pickle protocol.

Move pystate.h code surrounded by "#ifndef Py_LIMITED_API"
to a new Include/cpython/pystate.h header file.

* Move dictobject.h code surrounded by "#ifndef Py_LIMITED_API"
  to a new Include/cpython/dictobject.h header file.
* Add PyAPI_FUNC() to _PyDictView_New().
* Reorganize dictobject.h: move views and iterators at the end.

Move pylifecycle.h code surrounded by "#ifndef Py_LIMITED_API"
to a new Include/cpython/pylifecycle.h header file.

Move abstract.h code surrounded by "#ifndef Py_LIMITED_API"
to a new Include/cpython/abstract.h header file.

Regression introduced in e3ce6952 and 25b804a9, where the old parameter
update_tryorder to _synthesize was first ignored, then given the opposite
value in the attempt to fix bpo-31014.

Move pyerrors.h code surrounded by "#ifndef Py_LIMITED_API"
to a new Include/cpython/pyerrors.h header file.

Tolerate up to 30 ms, instead of 15 min, in other threads.