o Minor bugfixes (sandboxing):
    - When sandboxing is enabled, we could not write any stats to
      disk.  check_or_create_data_subdir("stats"), which prepares the
      private stats directory, calls check_private_dir(), which also
      opens and not just stats() the directory.  Therefore, we need to
      also allow open() for the stats dir in our sandboxing setup.
      Fixes bug 19556; bugfix on 0.2.5.1-alpha.