code: function(name, value) {
      var regexp, idx;
  
      // Remove the header from extraHeaders if present.
      regexp = new RegExp('^\\s*'+ name +'\\s*:','i');
      for (idx=0; idx<this.extraHeaders.length; idx++) {
        if (regexp.test(this.extraHeaders[idx])) {
          this.extraHeaders.splice(idx, 1);
        }
      }
  
      this.headers[Utils.headerize(name)] = (Array.isArray(value)) ? value : [value];
    }
docs: Replace the the given header by the given value.
  -param {String} name header name
  -param {String | Array} value header value