case sensitivity test

lib/request.js

@@ -368,6 +368,5 @@ req.__defineGetter__('stale', function(){
  */
 
 req.__defineGetter__('xhr', function(){
-  return this.header('X-Requested-With', '')
-    .toLowerCase() == 'xmlhttprequest';
+  return 'xmlhttprequest' == this.header('X-Requested-With', '').toLowerCase();
 });

test/req.xhr.js

@@ -20,6 +20,22 @@ describe('req', function(){
       })
     })
     
+    it('should case-insensitive', function(done){
+      var app = express();
+
+      app.use(function(req, res){
+        req.xhr.should.be.true;
+        res.end();
+      });
+
+      request(app)
+      .get('/')
+      .set('X-Requested-With', 'XMLHttpRequest')
+      .end(function(res){
+        done();
+      })
+    })
+    
     it('should return false otherwise', function(done){
       var app = express();