shutil.which() and distutils.spawn.find_executable() now use
os.confstr("CS_PATH") if available instead of os.defpath, if the PATH
environment variable is not set.

Don't use os.confstr("CS_PATH") nor os.defpath if the PATH
environment variable is set to an empty string to mimick Unix 'which'
command behavior.

Changes:

* find_executable() now starts by checking for the executable in the
  current working directly case. Add an explicit
  "if not path: return None".
* Add tests for PATH='' (empty string), PATH=':' and for PATHEXT.

It is changed from 16KiB to 64KiB.  The previous default value
is used since 1990.

coreutils chose 128 KiB as minimum buffer size for block device I/O.

But shutil.copyfileobj() can be used for non block devices.
So I choose more conservative value.

As my quick benchmark, performance difference between 64KiB and
128 KiB is up to ~5%.  On the other hand, performance difference
between 32 KiB and 64 KiB can be more than 10% when file is fully
buffered.

This is why 64 KiB is rational value.

bpo-35652: shutil.copytree(copy_function=...) erroneously pass DirEntry instead of path str (GH-11997)

Fix the documentation of copy2, as it does not copy file ownership (user and
group), only mode, mtime, atime and flags.

The original text was confusing to developers as it suggested that this
command is the same as 'cp -p', but according to cp(1), '-p' copies file
ownership as well.

Clarify which metadata is copied by shutil.copystat in its docstring.

bpo-33671
* use memoryview() with size == file size on Windows, see https://github.com/python/cpython/pull/7160#discussion_r195405230
* release intermediate (sliced) memoryview immediately
* replace "OSX" occurrences with "macOS"
* add some unittests for copyfileobj()

* 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

This speeds up it to 20-40%.

Thanks to Jelle Zijlstra for the patch.

This hides unwanted implementation details from tracebacks.

Imporoved the documentation and tests for make_archive() and unpack_archive().
Improved error handling when corresponding compress module is not available.
Brake circular dependency between shutil and tarfile modules.

Based on patch by Ville Skyttä.

reopened on Windows.  Added tests for fallbacks.

Issue #26801: Fix error handling in shutil.get_terminal_size(), catch
AttributeError instead of NameError. Patch written by Emanuel Barry.

test_shutil: skip the functional test using "stty size" command if
os.get_terminal_size() is missing.

for directories (including empty directories) in ZIP file.
Added test for comparing shutil.make_archive() with the "zip" command.

Patch by Eduardo Seabra and Thomas Kluyver.

An exception handler assumed that that OSError objects always have a
'winerror' attribute. That is not the case, so the exception handler
itself raised AttributeError when run on Linux (and, presumably, any
other non-Windows OS).

Patch by Greg Ward.

current directory in current directory.

Patch by Claudiu Popa.

Instead we'll just use the stdlib zipfile module.  Patch by Derek Chiang

on Windows if source name ends with os.altsep.

ModuleNotFoundError.