Add a third argument to http.cat to specify req headers.

lib/http.js

@@ -548,14 +548,19 @@ node.http.Client.prototype.put = function (uri, headers) {
 };
 
 
-exports.cat = function (url, encoding) {
+exports.cat = function (url, encoding, headers) {
   var promise = new node.Promise();
 
   encoding = encoding || "utf8";
 
   var uri = exports.parseUri(url);
+  headers = headers || {};
+  if (!headers["Host"] && uri.host) {
+    headers["Host"] = uri.host;
+  }
+
   var client = exports.createClient(uri.port || 80, uri.host);
-  var req = client.get(uri.path || "/", uri.host ? {"Host" : uri.host} : {});
+  var req = client.get(uri.path || "/", headers);
 
   client.addListener("error", function () {
     promise.emitError();