Import distribution in doctest

This both prevents the warning from surfacing during the tests and
ensures that no regressions occur.

Fixes GH issue #1612, bug introduced in commit 0902f02d

Remove use of splituser

added unittest for _download_git

Backend should not say that setuptools is needed to build

Fix issue with missing author metadata

Prior to this patch, if the author or author_email were omitted from
`setup`, a malformed `PKG-INFO` would be created.

Fix Travis test for pyc files in egg-info

`!` is a special character in YAML syntax, so this was being interpreted
as `grep pyc ...`, not `! grep pyc ...`

I've also added the same `pyc` test to the normal tests.

Release 40.6.0

Fix upload metadata

This comment is not used anywhere and `platform.dist()` is deprecated.

See CPython PR #10414: https://github.com/python/cpython/pull/10414
and bpo-35186: https://bugs.python.org/issue35186

Call os.path.normpath to normalize paths for comp

The `upload.show_response` feature was not added until Python 3. Rather
than backport it, it is now enabled only if supported.

This also adds a "smoke test" for the feature.