Change stacklevel in warnings.warn() for 'SO' key to 2.

Issue #7408: Forward port limited test from Python 2.7, fixing failing buildbot tests on BSD-based platforms.

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 #19544 and Issue #1180: Restore global option to ignore  ~/.pydistutils.cfg in Distutils, accidentally removed in backout of distutils2 changes.

Issue #19544 and Issue #6516: Restore support for --user and --group parameters to sdist command as found in Python 2.7 and originally slated for Python 3.2 but accidentally rolled back as part of the distutils2 rollback. Closes Issue #6516.

Merge with 3.3 for Issue #19544 and Issue #6286. Merge is untested. I was unable to test due to bab0cbf86835.

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

Patch by Oscar Benjamin.

Patch by Oscar Benjamin.