Hangul composition check boundaries are wrong for the second character
([0x1161, 0x1176) instead of [0x1161, 0x1176]) and third character ((0x11A7, 0x11C3)
instead of [0x11A7, 0x11C3]).

The existing doc had a number of info gaps and was a little hard to use.  This patch provides several quick-reference tables as well as examples.

python-gdb now catchs UnicodeDecodeError exceptions when calling
string().

python-gdb now catchs ValueError on read_var(): when Python has no
debug symbols for example.

* Enhance also format_duration(): work on integers and rounds towards
  +infinity (math.ceil).
* Write unit tests on format_duration()

Testing strategy: whitebox.

All the subinterpreter tests were disabled in gh-7513. This commit re-enables them, but leaves one bad test disabled. The test is partly causing problems because it makes assumptions about the availability of a high-level interpreters module (see PEP 554). So I'm disabling the test until such a high-level module is available.

string.Formatter auto-numbering feature was added in 3.4 and there
is no versionchanged note in its documentation, making the documentation
ambiguous about which version the feature is available.

* have shutil.copyfileobj use sendfile() if possible

* refactoring: use ctx manager

* add test with non-regular file obj

* emulate case where file size can't be determined

* reference _copyfileobj_sendfile directly

* add test for offset() at certain position

* add test for empty file

* add test for non regular file dst

* small refactoring

* leave copyfileobj() alone in order to not introduce any incompatibility

* minor refactoring

* remove old test

* update docstring

* update docstring; rename exception class

* detect platforms which only support file to socket zero copy

* don't run test on platforms where file-to-file zero copy is not supported

* use tempfiles

* reset verbosity

* add test for smaller chunks

* add big file size test

* add comment

* update doc

* update whatsnew doc

* update doc

* catch Exception

* remove unused import

* add test case for error on second sendfile() call

* turn docstring into comment

* add one more test

* update comment

* add Misc/NEWS entry

* get rid of COPY_BUFSIZE; it belongs to another PR

* update doc

* expose posix._fcopyfile() for OSX

* merge from linux branch

* merge from linux branch

* expose fcopyfile

* arg clinic for the win implementation

* convert path type to path_t

* expose CopyFileW

* fix windows tests

* release GIL

* minor refactoring

* update doc

* update comment

* update docstrings

* rename functions

* rename test classes

* update doc

* update doc

* update docstrings and comments

* avoid do import nt|posix modules if unnecessary

* set nt|posix modules to None if not available

* micro speedup

* update description

* add doc note

* use better wording in doc

* rename function using 'fastcopy' prefix instead of 'zerocopy'

* use :ref: in rst doc

* change wording in doc

* add test to make sure sendfile() doesn't get called aymore in case it doesn't support file to file copies

* move CopyFileW in _winapi and actually expose CopyFileExW instead

* fix line endings

* add tests for mode bits

* add docstring

* remove test file mode class; let's keep it for later when Istart addressing OSX fcopyfile() specific copies

* update doc to reflect new changes

* update doc

* adjust tests on win

* fix argument clinic error

* update doc

* OSX: expose copyfile(3) instead of fcopyfile(3); also expose flags arg to python

* osx / copyfile: use path_t instead of char

* do not set dst name in the OSError exception in order to remain consistent with platforms which cannot do that (e.g. linux)

* add same file test

* add test for same file

* have osx copyfile() pre-emptively check if src and dst are the same, otherwise it will return immedialtey and src file content gets deleted

* turn PermissionError into appropriate SameFileError

* expose ERROR_SHARING_VIOLATION in order to raise more appropriate SameFileError

* honour follow_symlinks arg when using CopyFileEx

* update Misc/NEWS

* expose CreateDirectoryEx mock

* change C type

* CreateDirectoryExW actual implementation

* provide specific makedirs() implementation for win

* fix typo

* skeleton for SetNamedSecurityInfo

* get security info for src path

* finally set security attrs

* add unit tests

* mimick os.makedirs() behavior and raise if dst dir exists

* set 2 paths for OSError object

* set 2 paths for OSError object

* expand windows test

* in case of exception on os.sendfile() set filename and filename2 exception attributes

* set 2 filenames (src, dst) for OSError in case copyfile() fails on OSX

* update doc

* do not use CreateDirectoryEx() in copytree() if source dir is a symlink (breaks test_copytree_symlink_dir); instead just create a plain dir and remain consistent with POSIX implementation

* use bytearray() and readinto()

* use memoryview() with bytearray()

* refactoring + introduce a new _fastcopy_binfileobj() fun

* remove CopyFileEx and other C wrappers

* remove code related to CopyFileEx

* Recognize binary files in copyfileobj()
...and use fastest _fastcopy_binfileobj() when possible

* set 1MB copy bufsize on win; also add a global _COPY_BUFSIZE variable

* use ctx manager for memoryview()

* update doc

* remove outdated doc

* remove last CopyFileEx remnants

* OSX - use fcopyfile(3) instead of copyfile(3)

...as an extra safety measure: in case src/dst are "exotic" files (non
regular or living on a network fs etc.) we better fail on open() instead
of copyfile(3) as we're not quite sure what's gonna happen in that
case.

* update doc

When attempting to base64-decode a payload of invalid length (1 mod 4),
properly recognize and handle it.  The given data will be returned as-is,
i.e. not decoded, along with a new defect, InvalidBase64LengthDefect.

The documentation for CERT_NONE, CERT_OPTIONAL, and CERT_REQUIRED were
misleading and partly wrong. It fails to explain that OpenSSL behaves
differently in client and server mode. Also OpenSSL does validate the
cert chain everytime. With SSL_VERIFY_NONE a validation error is not
fatal in client mode and does not request a client cert in server mode.
Also discourage people from using CERT_OPTIONAL in client mode.

Change suggested by Eryk Sun in a comment on PR 7137 after it was merged.

This is a separate PR because this does not backport to 3.6.

On Windows 8.1+ or 10, with DPI compatibility properties of the Python binary
unchanged, and a monitor resolution greater than 96 DPI, this should
make text and lines sharper. It should otherwise have no effect.

Using a magnifier, I determined that the improvement comes from horizontal and
lines being better lined up with the monitor pixels. I checked that this call causes
no problem on any Windows buildbot, including the Win7 buildbots. Unlike most
IDLE patches, this one can be easily reverted by users by removing a few lines,
at the top of idlelib/pyshell.py.

The docs claimed that a list of EmailMessage objects could be
passed to set_content(), but this was never implemented.

* Add declarations even if they are overridden by macros.
* Make the declaration and the definition of PyExceptionClass_Name
  consistent.

Before Python 3.6, os.path.abspath(None) used to report an AttributeError which was properly caught inside site.abs_paths, making it ignore __main__, one of sys.modules, which has __file__ and __cached__ set to None. With 3.6, os.path.abspath(None) raises TypeError instead which site.abs_path was not expecting.  This resulted in an uncaught exception if a user had PYTHONSTARTUP set and the application called site.main() which a number of third-party programs do.

A datetime object d is aware if d.tzinfo is not None and
d.tzinfo.utcoffset(d) does  not return None. If d.tzinfo is None,
or if d.tzinfo is not None but d.tzinfo.utcoffset(d) returns None,
 d is naive.

This commit ensures that instances with non-None d.tzinfo, but
d.tzinfo.utcoffset(d) returning None are treated as naive.

In addition, C acceleration code will raise TypeError if
d.tzinfo.utcoffset(d) returns an object with the type other than
timedelta.

* Updated the documentation.

Assume that the term "naive" is defined elsewhere and remove the
not entirely correct clarification.  Thanks, Tim.

Users can now click on context lines.