I deleted captured_stdout because its usage felt clumsy to me; better to
use stdlib?s test.support.captured_stdout in packaging and just write
out the code for d2.

I checked that adding the import of d2.tests.unittest at the top level
did not change the coverage accuracy (see comment in the source and the
history of the file for more info).

- Remove __main__ blocks obsoleted by pysetup
- Fix typo ?seperate?
- Add one test that was promised but not written
- Reorganize one file

I need this for some tests, and it makes code clearer.  This commit also
changes some assertEqual calls to use (actual, expected) order and fix
some pyflakes warnings.

These options were used to implement ?setup.py --name?,
?setup.py --version?, etc. which are now handled by the pysetup metadata
action or direct parsing of the setup.cfg file.

As a side effect, the Distribution class no longer accepts a 'url' key
in its *attrs* argument: it has to be 'home_page' or 'home-page' to be
recognized as a valid metadata field and passed down to the
dist.metadata object.

shutil, sysconfig, tarfile and their tests have been updated to the
latest 3.2 version (except for test_tarfile which is not backported yet)
and edited to be compatible with 2.4.

Duplicates added in util during the Great Update have been deleted, as
well as functions I removed recently in packaging.  Unneeded modules in
_backport have been deleted or moved to d2.compat.