o Major features (bootstrap):
    - Report the first connection to a relay as the earliest phases of
      bootstrap progress, regardless of whether it's a connection for
      building application circuits.  This allows finer-grained
      reporting of early progress than previously possible with the
      improvements of ticket 27169.  Closes tickets 27167 and 27103.
      Addresses ticket 27308.
    - Separately report the intermediate stage of having connected to
      a proxy or pluggable transport, versus succesfully using that
      proxy or pluggable transport to connect to a relay.  Closes
      tickets 27100 and 28884.