Test data for ar parsing and debsig-style signature checking are taken from
projects with which we are attempting to remain compatible.

- Test data for debsig-type signature checking are taken from the
  GPLv2-licensed `debsig-verify` project, last modified as of 2020-12-24.

- Test data for ar parsing are taken from the MIT-licensed ar library by Blake
  Smith, at https://github.com/blakesmith/ar, last modified as of 2019-02-19.

  - `long.a` is taken from https://cs.opensource.google/go/x/tools/+/master:go/gccgoexportdata/testdata/long.a

None of this data is included in compiled binaries, so the licensing terms for
binaries compiled with or from go-debian are not modified.
