revalidate (::Utils::HttpUtil::CachedObject)

    # File lib/rbot/core/utils/httputil.rb, line 252
        def revalidate(resp = self.response)
          @count = 0
          self.use
          self.date = resp.key?('date') ? Time.httpdate(resp['date']) : Time.now

          cc = resp['cache-control']
          if cc && (cc =~ /max-age=(\d+)/)
            self.expires = self.date + $1.to_i
          elsif resp.key?('expires')
            self.expires = Time.httpdate(resp['expires'])
          elsif lm = resp['last-modified']
            delta = self.date - Time.httpdate(lm)
            delta = 10 if delta <= 0
            delta /= 5
            self.expires = self.date + delta
          else
            self.expires = self.date + 300
          end
          # self.expires = Time.now + 10 # DEBUG
          debug "expires on #{self.expires}"

          return true
        end