o Major bugfixes (directory authorties):
    - When computing weight parameters, behave more robustly in the
      presence of a bad bwweightscale value.  Previously, the
      authorities would crash if they agreed on a sufficiently browken
      weight_scale value: now, they use a reasonable default and carry
      on. Partial fix for 5786; bugfix on 0.2.2.17-alpha.