Issue #27960: Revert state to 675e20c38fdac6, backing out all changes by developed for Issue #12885.

Several test cases in distutils use PyPIRCCommandTestCase as
their base class and as a result of that the following tests
were ran more than once:

* test_server_registration
* test_server_empty_registration
* test_config_interpolation

This commit moves the infrastructure used by other tests
into a new BasePyPIRCCommandTestCase class.

I noticed that there is no test for this feature while doing
triaging work on pypa/pypi-legacy.

Issue #27048: Prevents distutils failing on Windows when environment variables contain non-ASCII characters

Initial patch by ingrid.

  Patch by Xavier de Gaye.

Initial patch by Claudiu Popa.

Most fixes to Doc/ and Lib/ directories by Ville Skyttä.

Issue #20120: Use RawConfigParser for .pypirc parsing, removing support for interpolation unintentionally added with move to Python 3. Behavior no longer does any interpolation in .pypirc files, matching behavior in Python 2.7 and Setuptools 19.0.

It was renamed to 'license' in 178d19cff163.

Patch by Augustin Laville.

As of Xcode 7, SDKs for Apple platforms now include textual-format stub
libraries whose file names have a .tbd extension rather than the
standard OS X .dylib extension.  The Apple compiler tool chain handles
these stub libraries transparently and the installed system shared libraries
are still .dylibs.  However, the new stub libraries cause problems for
third-party programs that support building with Apple SDKs and make
build-time decisions based on the presence or paths of system-supplied
shared libraries in the SDK.  In particular, building Python itself with
an SDK fails to find system-supplied libraries during setup.py's build of
standard library extension modules.  The solution is to have
find_library_file() in Distutils search for .tbd files, along with
the existing types (.a, .so, and .dylib).  Patch by Tim Smith.