o Minor bugfixes (performance):
    - Avoid calling protocol_list_supports_protocol() from inside tight loops
      when running with cached routerinfo_t objects.  Instead,
      summarize the relevant protocols as flags in the routerinfo_t, as we do
      for routerstatus_t objects.  This change simplifies our code a little,
      and saves a large amount of short-term memory allocation operations.
      Fixes bug 25008; bugfix on 0.2.9.4-alpha.