I change the PR title, but the commit message is still miss leading.

oops, fixed.

rebased to use qhull 2020.2. @ianthomas23 feel free to force-push over the last PR to become recorded as author; I copy pasted your qhull_wrap.c from #16571 but couldn't cherry pick the commit as that change was not standalone.

@anntzer for your information: You can acknowledge other authors via the commit message:
https://docs.github.com/en/free-pro-team@latest/github/committing-changes-to-your-project/creating-a-commit-with-multiple-authors#creating-co-authored-commits-on-the-command-line

nice, thanks.

@ianthomas23 feel free to force-push over the last PR to become recorded as author; I copy pasted your qhull_wrap.c from #16571 but couldn't cherry pick the commit as that change was not standalone.

@anntzer I was thinking that if my name isn't on it, I can't be blamed if anything goes wrong with it in future! But it looks like you have already credited/blamed me 😃

Do we need to consider what to do with qhull's licence file (COPYING.txt)? We used to keep a copy in the extern directory with the source code, but if we are downloading the code on demand I don't know if a static copy is required or not.

I'll let @tacaswell decide on the legal stuff :)

It will be built into the wheels, so we need to keep the license. Clause 2 says you must provide the license for any copies, so we should copy it into LICENSE/ either permanently or on unpack.

I now copy the license on unpack, and also just unified the codepaths with the freetype download/cache codepath.

The test failures are spurious I think...