tor/changes/bug13963-decrease-if-modified-since-delay

  o Minor bugfixes:
    - When V3AuthVotingInterval is low, decrease the delay on the
      If-Modified-Since header passed to directory servers.
      This allows us to obtain consensuses promptly when the consensus
      interval is very short.
      This assists in bootstrapping a testing Tor network.
      Fixes bugs 13718 & 13963.