o Major bugfixes (security, directory authority):
    - When computing directory thresholds, ignore any rejected-as-sybil
      nodes during the computation so that they can't influence Fast,
      Guard, etc. Fixes bug 8146.

    - When computing thresholds for flags, never let the threshold for
      the Fast flag to 4096 bytes. Fixes bug 8145.
    - Do not consider nodes with extremely low bandwidths when deciding
      thresholds for various directory flags. Another fix for 8145.

    - When marking a node as a likely sybil, reset its uptime metrics
      to zero, so that it cannot time towards getting marked as Guard,
      Stable, or HSDir. Fix for bug 8147.