  o Major bugfixes (congestion control):
    - Implement RFC3742 Limited Slow Start. Congestion control was
      overshooting the congestion window during slow start, particularly for
      onion service activity. With this fix, we now update the congestion
      window more often during slow start, as well as dampen the exponential
      growth when the congestion window grows above a capping parameter.
      This should reduce the memory increases guard relays were seeing, as
      well as allow us to set lower queue limits to defend against
      ongoing DoS attacks. Fixes bug 40642; bugfix on 0.4.7.5-alpha.
