Fix memory leaks in asyncio ProactorEventLoop on overlapped operation
failures.

Changes:

* Implement the tp_traverse slot in the _overlapped.Overlapped type
  to help to break reference cycles and identify referrers in the
  garbage collector.
* Always clear overlapped on failure: not only set type to
  TYPE_NOT_STARTED, but release also resources.

Document that the time.CLOCK_MONOTONIC_RAW constant
is now also available on macOS 10.12.
Co-authored-by: Ricardo Fraile <rfraile@rfraile.eu>

* asyncio: __del__() keep reference to warnings.warn

The __del__() methods of asyncio classes now keep a strong reference
to the warnings.warn() to be able to display the ResourceWarning
warning in more cases. Ensure that the function remains available if
instances are destroyed late during Python shutdown (while module
symbols are cleared).

* Rename warn parameter to _warn

"_warn" name is a hint that it's not the regular warnings.warn()
function.

* _wait_for_handle(), _register() and _unregister() methods of
  IocpProactor now raise an exception if closed
* Add "closed" to IocpProactor.__repr__()
* Simplify IocpProactor.close()

Fix a memory leak in asyncio in the ProactorEventLoop when ReadFile()
or WSASend() overlapped operation fail immediately: release the
internal buffer.

Also adds extra steps to the CI build for Windows on Azure Pipelines to validate that the various layouts at least execute.

As in title, expose C `raise` function as `raise_function` in `signal` module. Also drop existing `raise_signal` in `_testcapi` module and replace all usages with new function.


https://bugs.python.org/issue35568

bpo-32622, bpo-35682: Fix asyncio.ProactorEventLoop.sendfile(): don't
attempt to set the result of an internal future if it's already done.

Fix asyncio _ProactorBasePipeTransport._force_close(): don't set the
result of _empty_waiter if it's already done.

This module is built by _asyncio.vcxproj and does not need to be included in pythoncore.

test.pythoninfo now logs information of all clocks, not only time.time() and
time.perf_counter().

test_asyncio/test_sendfile.py now resets the event loop policy using
tearDownModule() as done in other tests, to prevent a warning when
running tests on Windows.

Fix an assertion error in format() in debug build for floating point
formatting with "n" format, zero padding and small width. Release build is
not impacted. Patch by Karthikeyan Singaravelan.

* bpo-35660: IDLE: Remove * import from window.py

* sys was being imported through the *, so also added an import sys.

* Update 2019-01-04-19-14-29.bpo-35660.hMxI7N.rst

Anyone who wants details can check the issue, where I added the point about the sys import bug.

https://bugs.python.org/issue35631

bpo-31450: Remove documentation mentioning that subprocess's child_traceback is available with the parent process (GH-11422)

closes bpo-35643: Fix a SyntaxWarning: invalid escape sequence in Modules/_sha3/cleanup.py (GH-11411)

Revert "bpo-35603: Escape table header of make_table output that can cause potential XSS. (GH-11341)" (GH-11356)

This reverts commit 78de0119.

* bpo-35588: Implement mod and divmod operations for Fraction type by spelling out the numerator/denominator calculation, instead of instantiating and normalising Fractions along the way. This speeds up '%' and divmod() by 2-3x.

* bpo-35588: Also reimplement Fraction.__floordiv__() using integer operations to make it ~4x faster.

* Improve code formatting.
Co-Authored-By: scoder <stefan_ml@behnel.de>

* bpo-35588: Fix return type of divmod(): the result of the integer division should be an integer.

* bpo-35588: Further specialise __mod__() and inline the original helper function _flat_divmod() since it's no longer reused.

* bpo-35588: Add some tests with large numerators and/or denominators.

* bpo-35588: Use builtin "divmod()" function for implementing __divmod__() in order to simplify the implementation, even though performance results are mixed.

* Rremove accidentally added empty line.

* bpo-35588: Try to provide more informative output on test failures.

* bpo-35588: Improve wording in News entry.
Co-Authored-By: scoder <stefan_ml@behnel.de>

* Remove stray space.