The current code in find_on_path is doing a lot of stat() calls which are
actually useless and prone to race conditions.

As described in Python documentation
(https://docs.python.org/3/library/os.html#os.access), os.access must not be
used before opening a file. Same goes for a directory.

This patch removes those checks by handling exceptions correctly when using
os.listdir() instead, which improves pkg_resources import time.

Rename [wheel] section to [bdist_wheel] as the former is legacy

Fix exception on mingw built Python 2

msvc9compiler doesn't like being imported on mingw built Python. It
throws DistutilsPlatformError, so catch it.

Fixes #1118

The exception is caused by the VCForPython27 monkey patch. It's not needed on mingw built Python. Disable it and avoid the import by using the same function that `distutils` uses to decide it's running on a mingw built Python.

Fixes #1118

fix requires handling when using setup.cfg

Better detect unpacked eggs

Do not assume a directory named in `.egg` is an egg, unless it has an
actual egg metadata directory.

Closes #462

But our tests do, one that provides `--no-wheel`.

Directory used by setuptools to auto-install dependencies

travis: fix deployment

update Travis builds

tests: disable pytest-flake8 on Python 2.6

Fix `test` command handling of `extras_require`

Python 2.6 support has been official dropped from
flake8 for some time, and broken since 3.4.0.

Update to the future defaults: `dist: trusty`.

Also install platform specific requirements in `extras_require`.

do not strip empty sections in `extras_require`

Revert "fix `install_requires` handling of extras"

This reverts commit a3ec721e.