help.github.com seems to have a bug where HEAD on a redirected page
returns 404. This causes tools/test-documentation to fail. Fix it by
skipping the redirects.
Signed-off-by: Anders Kaseorg <andersk@mit.edu>
This is what the Sphinx docs recommend when you actually don't want
the page to be included in navigation:
http://www.sphinx-doc.org/en/stable/markup/toctree.html
And now that we have `eval_rst`, we're able to take advantage of it!
One difference between doing this and the old way of making "hidden"
toctree entries is that with the latter, the "previous" and "next"
links at the bottom of each page would thread through the hidden
entries; which gets kind of confusing when they don't appear in the nav.