def expired?
      return true unless @expires
      return false if @expires > Time.now
      return true if @renewer.nil?
      renew(@renewer)
      return true unless @expires
      return @expires < Time.now
    end
def expired?
      return true unless @expires
      return false if @expires > Time.now
      return true if @renewer.nil?
      renew(@renewer)
      return true unless @expires
      return @expires < Time.now
    end
Has this tuple expired? (true/false).

 A tuple has expired when its expiry timer based on the +sec+ argument to
 #initialize runs out.