tor/changes/bug-15642-default-fallback-default-dirs

  o Minor bugfixes (configuration, unit tests):
    - Only add the default fallback directories when the DirAuthorities,
      AlternateDirAuthority, and FallbackDir directory config options
      are set to their defaults.
      The default fallback directory list is currently empty, this fix
      will only change tor's behaviour when it has default fallback
      directories.
      Includes unit tests for consider_adding_dir_servers().
      Fixes bug 15642; bugfix on 90f6071d8dc0 in 0.2.4.7-alpha.
      Patch by "teor".