code: function(name) {
      var regexp, idx,
        length = this.extraHeaders.length;
  
      if (this.headers[Utils.headerize(name)]) {
        return true;
      } else {
        regexp = new RegExp('^\\s*'+ name +'\\s*:','i');
        for (idx=0; idx<length; idx++) {
          if (regexp.test(this.extraHeaders[idx])) {
            return true;
          }
        }
      }
  
      return false;
    }
docs: Verify the existence of the given header.
  -param {String} name header name
  -returns {boolean} true if header with given name exists, false otherwise