Fix GH#325: Allow to pass None as a timeout value to disable timeout logic.

Change written by Andrew Svetlov and merged by Guido van Rossum.

On Python 3.3, use aliases:

* PyMem_RawMalloc = PyMem_Malloc
* PyMem_RawFree = PyMem_Free

These aliases are not need in Python 3.5, but this change makes synchronization
of code base simpler.

Also change BufferedReader.writable() and BufferedWriter.readable() to always
return False.

Affected classes are generic sequence iterators, iterators of str, bytes,
bytearray, list, tuple, set, frozenset, dict, OrderedDict, corresponding
views and os.scandir() iterator.

Reported by Matthew Cole on docs@p.o.

Use the default timeout of 30 seconds to avoid blocking forever.

* Fix test_os.BytesWalkTests on Windows
* Mimick better the reference os.DirEntry on Windows
* _DummyDirEntry now caches os.stat() result
* _DummyDirEntry constructor now tries to get os.stat()
* Fix os._DummyDirEntry.is_symlink(), don't follow symbolic links:
  use os.stat(path, follow_symlinks=False).

_Call is a subclass of tuple (changeset 3603bae63c13 only works
for classes) so we need to implement __ne__ ourselves.

Patch by Andrew Plummer.

If you pass -1, the callable can take any number of arguments.

Added tests to verify the behavior.

Initial patch by Cédric Krier.

The behaviour of the close method is tested by ClosedCurTests
in Lib/sqlite3/test/dbapi.py.

This is basically a backport of https://github.com/ghaering/pysqlite/issues/73.

Fix a warning on Windows 64-bit.

Write the module name rather than <module> in the error message, if module has
no __file__ attribute (ex: package).

* multiprocessing: open file with closefd=False to avoid ResourceWarning
* _test_multiprocessing: open file with O_EXCL to detect bugs in tests (if a
  previous test forgot to remove TESTFN)
* test_sys_exit(): remove TESTFN after each loop iteration

Initial patch written by Serhiy Storchaka.

Use -Wd comment line option to log the ResourceWarning.

Issue #26161: Use Py_uintptr_t instead of void* for atomic pointers in
pyatomic.h. Use atomic_uintptr_t when <stdatomic.h> is used.

Using void* causes compilation warnings depending on which implementation of
atomic types is used.

Declare the function even if thread support is disabled.

Issue #21925: warnings.formatwarning() now catches exceptions on
linecache.getline(...) to be able to log ResourceWarning emitted late during
the Python shutdown process.

test_warnings: only run test_improper_option() and test_warnings_bootstrap()
once. The unit test doesn't depend on self.module.

Issue #26588: Enhance assertion in set_reentrant()

Issue #26588: Fix _tracemalloc start/stop: don't play with the reentrant flag.

set_reentrant(1) fails with an assertion error if tracemalloc_init() is called
first in a thread A and tracemalloc_start() is called second in a thread B. The
tracemalloc is imported in a thread A. Importing the module calls
tracemalloc_init(). tracemalloc.start() is called in a thread B.