o Minor bugfixes (circuit build timeout):
    - Improve the accuracy of our circuit build timeout calculation for 60%,
      70%, and 80% build rates for various guard choices. We now use a maximum
      likelihood estimator for Pareto parameters of the circuit build time
      distribution, instead of a "right-censored estimator". This causes
      clients to ignore circuits that never finish building in their timeout
      calculations. Previously, clients were counting such unfinished circuits
      as having the highest possible build time value, when in reality these
      circuits most likely just contain relays that are offline. We also now
      wait a bit longer to let circuits complete for measurement purposes,
      lower the minimum possible effective timeout from 1.5 seconds to 10ms,
      and increase the resolution of the circuit build time histogram from
      50ms bin widths to 10ms bin widths. Additionally, we alter our estimate
      Xm by taking the maximum of the top 10 most common build time values
      of the 10ms histogram, and compute Xm as the average of these.
      Fixes bug 40168; bugfix on 0.2.2.14-alpha.