o Minor bugfixes (directory cache):
    - When a consensus diff calculation is only partially successful, only
      record the successful parts as having succeeded. Partial success
      can happen if (for example) one compression method fails but
      the others succeed. Previously we misrecorded all the calculations as
      having succeeded, which would later cause a nonfatal assertion failure.
      Fixes bug 24086; bugfix on 0.3.1.1-alpha.