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

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

   _sysconfigdata module too.

  plat-$(PLATFORM_TRIPLET).
  Rename the config directory (LIBPL) from config-$(LDVERSION) to
  config-$(LDVERSION)-$(PLATFORM_TRIPLET).
  Install the platform specifc _sysconfigdata module into the platform
  directory and rename it to include the ABIFLAGS.

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.