Closes #13995.

Initial patch by Johannes Vogel.

Patch by Hynek Schlawack.

Patch by Suman Saha.

Patch by Suman Saha.

Issue #10287: nntplib now queries the server's CAPABILITIES first before sending MODE READER, and only sends it if not already in READER mode.
Patch by Hynek Schlawack.

directory tree instead of overwriting the input files.  Adds three command
line options: -o/--output-dir, -W/--write-unchanged-files and --add-suffix.

Feature backports into stable release branches for 2to3 are allowed by
a special exemption:
 http://mail.python.org/pipermail/python-dev/2011-December/115089.html

Closes #9750

Issue #10287: nntplib now queries the server's CAPABILITIES again after authenticating (since the result may change, according to RFC 4643).
Patch by Hynek Schlawack.

The code used to call os.path.join to build a regex but without escaping
the backslash, which lead to test failures on Windows.  Antoine Pitrou
fixed it in 0a94e2f807c7 by enhancing the code to accept both / and \,
with proper escaping, but in my opinion this goes against the distutils
feature freeze, hence this change.

If I grepped correctly, this was the last outdated place.

Also, give a more helpful error message when opened with an invalid mode string.

Distutils-based packages with C extension modules may fail because
Apple has removed gcc-4.2, the version used to build python.org
64-bit/32-bit Pythons.  If the user does not explicitly override
the default C compiler by setting the CC environment variable,
Distutils will now attempt to compile extension modules with clang
if gcc-4.2 is required but not found. Also as a convenience, if
the user does explicitly set CC, substitute its value as the default
compiler in the Distutils LDSHARED configuration variable for OS X.
(Note, the python.org 32-bit-only Pythons use gcc-4.0 and the 10.4u
SDK, neither of which are available in Xcode 4.  This change does not
attempt to override settings to support their use with Xcode 4.)

Reedy.