o Major bugfixes (congestion control):
    - Avoid incrementing the congestion window when the window is not
      fully in use. Thia prevents overshoot in cases where long periods
      of low activity would allow our congestion window to grow, and
      then get followed by a burst, which would cause queue overload.
      Also improve the increment checks for RFC3742. Fixes bug 40732;
      bugfix on 0.4.7.5-alpha.