def web_modification_time(local_url)
      resp = nil
      Net::HTTP.start(local_url.host, 80) do |http|
        resp = http.head(local_url.path)
      end
      resp['Last-Modified'].nil? ? Time.at(0) : Time.parse(resp['Last-Modified'])
    end
def web_modification_time(local_url)
      resp = nil
      Net::HTTP.start(local_url.host, 80) do |http|
        resp = http.head(local_url.path)
      end
      resp['Last-Modified'].nil? ? Time.at(0) : Time.parse(resp['Last-Modified'])
    end
Returns the last-modified time from the remote server. Assumes the remote server knows how to
 do this. Returns the epoch if the remote is dense.