  o Minor bugfixes (directory warnings):
    - When fetching extrainfo documents, compare their SHA256 digests
      and Ed25519 signing key certificates
      with the routerinfo that led us to fetch them, rather than
      with the most recent routerinfo. Otherwise we generate many
      spurious warnings about mismatches. Fixes bug 17150; bugfix
      on 0.2.7.2-alpha.
