o Minor bugfixes (directory download scheduling):
    - Remove the maximum delay on exponential-backoff scheduling.
      Since we now allow an infinite number of failures (see ticket
      20536), we must now allow the time to grow longer on each failure.
      Fixes part of bug 20534; bugfix on 0.2.9.1-alpha.
    - Use initial delays and decrements in download scheduling closer to
      those from 0.2.8. Fixes another part of bug 20534; bugfix on
      0.2.9.1-alpha.