未处理其他错误码的情况，简单的判断是否有centent-length不是很妥当

[zhxiaom5]

//add by wangfeng
    if(get_content_length(txnp, txn_state) == false){

      DEBUG_LOG("warnning. response is not include content_length, attempting to disable cache write.");

      TSHttpHdrReasonSet(response, resp_hdr, "oxwangfeng",10);

      TSHandleMLocRelease(response, resp_hdr, NULL);
      return;
    }

这样处理不太合适吧，不知道贵司cdn还好不，这地方的逻辑，会导致304回源有问题吧。