It might work with earlier versions, but I have not tested that yet.

to avoid conflicts with the original files when -I includes the original
sources.

see https://httpwg.org/specs/rfc7231.html#header.content-location

- use the new dedicated field to store the location such that we can
  still properly send metadata with responses to HEAD requests

- always send the location, not just for GET 301s

- no need to generate a 410 as long as we still have the metadata

- retire TUS_REDIRECT type, we do not need it (files with a redirect
  remain intact).

This implies a file version change.

Later in the project, we would want to upgrade existing files, but for
now, I assume the number of users be so close to zero that we can put
the burdon on them to lose their existing uploads once during upgrade.

this could lead to later assertion failures when the tus directory
contained failes not fit for loading (e.g. wrong size/magic etc)
because valid files would be munmap()ed.

I had constified struct vmod_blobdigest_digest just before release,
which does not work. I have not understood why this did not show up as a
compile error before.