Because we do not include setuptools in our build requirements and there
is no mechanism for a PEP 517 backend to bootstrap itself, setuptools
cannot use setuptools.build_meta as its backend, and cannot use PEP 517
to build itself.

Additionally, if you specify build-backend, it is impossible to disable
PEP 517 builds with pip's --no-use-pep517 flag.

tweak #1644 workaround to fix `test_pip_upgrade_from_source`

Bugfix/1663 restore port

Ensure port is included in package-index

Ensure a specified port in package_index isn't lost in the parse/unparse of the URL when auth is present. Fixes #1663.

Prefer native strings on Python 2 when reading config files.

tests: minor cleanup

Explicitly exclude `pyproject.toml` so it's never added (e.g. because `setuptools_scm` is used).

Disallow parent path traversal in resource paths, part 1 (deprecation)

Setuptools will install licenses if included in setup.cfg

improve encoding handling for `setup.cfg`

tests: temporary pin pip to fix the Python 2.7 job

Given that the config file parsing functionality is unlikely to change upstream, just incorporate the functionality directly.