o Major features:
    - Add a new FallbackDir option to use when we can't use a directory
      from the consensus (either because we lack a consensus, or because
      they're all down).  Currently, all authorities are fallbacks by
      default, and there are no other default fallbacks, but that will
      change.  This option will allow us to give clients a longer list
      of servers to try to get a consensus from when first connecting to
      the Tor network, and thereby reduce load on the directory
      authorities. Implements proposal 206, "Preconfigured directory
      sources for bootstrapping". Closes bug 572.

  o Removed features:
    - Drop the old FallbackNetworkstatus option: we never got it working
      well enough to use it. Closes bug 572.