o Minor features:
    - Clear the high bit on curve25519 public keys before passing them to
      our backend, in case we ever wind up using a backend that doesn't do
      so itself. If we used such a backend, and *didn't* clear the high bit,
      we could wind up in a situation where users with such backends would
      be distinguishable from users without. Fix for bug 8121; bugfix on
      0.2.4.8-alpha.