auto_chmod subscripts exceptions on py3

if ev is an OSError (as it's likely to be), you can not subscript it on py3

six.reraise(et, (ev[0], ev[1] + (" %s %s" % (func, arg))))

This was in some custom code doing a pep 517 build (from source) on pytest-black 0.3.8 on python 3.6. I am not sure exactly what was a symlink.

Traceback (most recent call last):
  File "<omit>/python3.6/shutil.py", line 488, in rmtree
    raise OSError("Cannot call rmtree on a symbolic link")
OSError: Cannot call rmtree on a symbolic link
During handling of the above exception, another exception occurred:
  File "<omit>/_pyfi_pep517_bootstrap.py", line 19, in <module>
    wheel_filename = pep517_builder.build_wheel(wheel_dir)
  File "<omit>/python3.6/site-packages/setuptools/build_meta.py", line 209, in build_wheel
    wheel_directory, config_settings)
  File "<omit>/python3.6/site-packages/setuptools/build_meta.py", line 194, in _build_with_temp_dir
    self.run_setup()
  File "<omit>/python3.6/site-packages/setuptools/build_meta.py", line 237, in run_setup
    self).run_setup(setup_script=setup_script)
  File "<omit>/python3.6/site-packages/setuptools/build_meta.py", line 142, in run_setup
    exec(compile(code, __file__, 'exec'), locals())
  File "setup.py", line 44, in <module>
    entry_points={"pytest11": ["black = pytest_black"]},
  File "<omit>/python3.6/site-packages/setuptools/__init__.py", line 144, in setup
    _install_setup_requires(attrs)
  File "<omit>/python3.6/site-packages/setuptools/__init__.py", line 139, in _install_setup_requires
    dist.fetch_build_eggs(dist.setup_requires)
  File "<omit>/python3.6/site-packages/setuptools/dist.py", line 720, in fetch_build_eggs
    replace_conflicting=True,
  File "<omit>/python3.6/site-packages/pkg_resources/__init__.py", line 782, in resolve
    replace_conflicting=replace_conflicting
  File "<omit>/python3.6/site-packages/pkg_resources/__init__.py", line 1065, in best_match
    return self.obtain(req, installer)
  File "<omit>/python3.6/site-packages/pkg_resources/__init__.py", line 1077, in obtain
    return installer(requirement)
  File "<omit>/python3.6/site-packages/setuptools/dist.py", line 787, in fetch_build_egg
    return cmd.easy_install(req)
  File "<omit>/python3.6/site-packages/setuptools/command/easy_install.py", line 679, in easy_install
    return self.install_item(spec, dist.location, tmpdir, deps)
  File "<omit>/python3.6/contextlib.py", line 99, in __exit__
    self.gen.throw(type, value, traceback)
  File "<omit>/python3.6/site-packages/setuptools/command/easy_install.py", line 643, in _tmpdir
    os.path.exists(tmpdir) and rmtree(rmtree_safe(tmpdir))
  File "<omit>/python3.6/site-packages/setuptools/command/easy_install.py", line 2277, in rmtree
    return shutil.rmtree(path, ignore_errors, onerror)
  File "<omit>/python3.6/shutil.py", line 490, in rmtree
    onerror(os.path.islink, path, sys.exc_info())
  File "<omit>/python3.6/site-packages/setuptools/command/easy_install.py", line 1729, in auto_chmod
    six.reraise(et, (ev[0], ev[1] + (" %s %s" % (func, arg))))
TypeError: 'OSError' object is not subscriptable

Start at setuptools/command/easy_install.py, specifically the auto_chmod entry point shown in the traceback, and compare its exception handling with Python 3 OSError behavior. Reproduce the symbolic-link cleanup failure if possible; done means the original error is reraised with the function and argument context without causing a TypeError.