whereto: support [codes] in .htaccess

[Eric Fried]

(Erroneously opened this as https://storyboard.openstack.org/#!/story/2006943 before noticing we're back to LP.)

Discovered via [1], which tried to do a redirectmatch to a target with an #anchor in it.

That wouldn't work (though we can't prove it in CI because the CI docs build doesn't appear to process .htaccess -- which I suppose makes sense as that would entail restarting the build server's httpd? not sure) unless you added the [NE] flag [2]. But (aside from not being able to tell if it worked until published) whereto hates that:

 docs run-test: commands[4] | whereto doc/build/html/.htaccess doc/test/redirect-tests.txt
 Traceback (most recent call last):
  File "/home/efried/openstack/nova/.tox/docs/bin/whereto", line 8, in <module>
    sys.exit(main())
  File "/home/efried/openstack/nova/.tox/docs/lib/python3.6/site-packages/whereto/app.py", line 195, in main
    ruleset.add(linenum, *params)
  File "/home/efried/openstack/nova/.tox/docs/lib/python3.6/site-packages/whereto/rules.py", line 113, in add
    rule = self._factories[rule_type](linenum, *params)
  File "/home/efried/openstack/nova/.tox/docs/lib/python3.6/site-packages/whereto/rules.py", line 77, in __init__
    super(RedirectMatch, self).__init__(linenum, *params)
  File "/home/efried/openstack/nova/.tox/docs/lib/python3.6/site-packages/whereto/rules.py", line 50, in __init__
    raise ValueError('Could not understand rule {}'.format(params))
 ValueError: Could not understand rule ('redirectmatch', '301', '^/nova/([^/]+)/admin/manage-users.html$', '/nova/$1/admin/arch.html#projects-users-and-roles', '[NE]')
 ERROR: InvocationError for command /home/efried/openstack/nova/.tox/docs/bin/whereto doc/build/html/.htaccess doc/test/redirect-tests.txt (exited with code 1)

So this RFE is to beef up whereto to understand these codes. (To be fair, I'm not sure if it should really understand them -- e.g., know that a redirect to /foo.html#bar is /foo.html%23bar without [NE] and /foo.html#bar with it -- or if it should just retain its existing logic but not blow up when there's a fifth field on the .htaccess line. Baby steps?)

[1] https://review.opendev.org/#/c/695779/1/doc/source/_extra/.htaccess@80
[2] http://httpd.apache.org/docs/2.2/rewrite/flags.html#flag_ne