When running external programs such as a C compiler and getting an
error code, distutils only prints the program name.  With this change,
one can get the full command line by setting the DISTUTILS_DEBUG
environment variable.

This should have no compatibility issues, unless there are tools
that depend on the exact format of distutils debug messages.

Thanks to Amaury Forgeot d’Arc and Philip J. Eby.

Patch by Berker Peksag.

Fix urllib.request.build_opener mocking in test_distutils (should fix some random buildbot failures)

Issue #19544 and Issue #6286: Restore use of urllib over http allowing use of http_proxy for Distutils upload command, a feature accidentally lost in the rollback of distutils2.

Issue 19544 and Issue #7457: Restore the read_pkg_file method to distutils.dist.DistributionMetadata accidentally removed in the undo of distutils2.

Issue #19286: Adding test demonstrating the failure when a directory is found in the package_data globs.

Patch by Oscar Benjamin.