anchor.diff:               transformRequest: transformRequest, transformResponse: transformResponse,
                cache: cache, timeout: timeout);
   
  +  /**
  +   * Shortcut method for POST requests.  See [call] for a complete description
  +   * of parameters.
  +   */
     async.Future<HttpResponse> post(String url, String data, {
       Map<String, dynamic> params,
       Map<String, String> headers,
  
positive.code:              transformRequest: transformRequest, transformResponse: transformResponse,
               cache: cache, timeout: timeout);
  
    async.Future<HttpResponse> delete(String url, {
      String data,
      Map<String, dynamic> params,
  
negative.code:   }
  
    Function _headersGetter(Map headers) {
      var headersObj;
  
      return ([String name]) {
        if (headersObj == null) {
          headersObj = {};
          headers.forEach((k,v) {
            headersObj[k.toLowerCase()] = v;
          });
        }
  
        if (name != null) {
          name = name.toLowerCase();
          if (!headersObj.containsKey(name)) return null;
          return headersObj[name];
        }
  
        return headersObj;
      };
    }
  }
  