At least, I suppose it was incorrect.  It won't build anywhere it has not
already built.  I don't know how it built where it already built.

why make it a plugin, then, you may ask.
or perhaps you may not ask.

overrides

They're not necessary on newly selected nixpkgs revision.

The layer above will have to make sure that it is.

This gives us the merged version of Ristretto support.

This format for the file can be generated automatically using something like:

  nix-prefetch-github \
    --nix \
    --rev $(git rev-parse HEAD) \
    PrivateStorageio ZKAPAuthorizer > /path/to/zkapauthorizer-repo.nix

run in in a checkout of ZKAPAuthorizer

only useful for debugging failed test runs

The issuer runs.  Helpers to poke the right API calls into the right place
forthcoming...

It is better than what we have here and duplicating it is sad.  ZKAPAuthorizer
also has much tighter binding to Tahoe-LAFS version than anything in this
repository so it makes sense to let it dictate that detail.

Also bump the version being used.  This will be important in a minute.