修复当memcached不可用时，会有一个cookie对象undefined的错误

@@ -76,6 +76,13 @@ app.use(bodyParser.urlencoded({
 app.use(cookieParser());
 app.use(compression());
 
+const sessionStore = new MemcachedStore({
+    hosts: config.memcache.session,
+    prefix: 'yohobuy_session:',
+    reconnect: 5000,
+    timeout: 1000,
+    retries: 0
+});
 app.use(memcachedSession({
     proxy: true,
     resave: false,
@@ -87,20 +94,14 @@ app.use(memcachedSession({
         domain: 'yohobuy.com',
         httpOnly: false
     },
-    store: new MemcachedStore({
-        hosts: config.memcache.session,
-        prefix: 'yohobuy_session:',
-        reconnect: 5000,
-        timeout: 1000,
-        retries: 0
-    })
+    store: sessionStore
 }));
 
 app.use(cookieSession({
     requestKey: 'session2',
     cookieName: 'yohobuy_session_cookie',
     secret: '82dd7e724f2c6870472c89dfa43cf48d',
-    domain: config.cookieDomain
+    domain: 'yohobuy.com'
 }));
 
 app.use((req, res, next) => {
@@ -118,6 +119,10 @@ app.use((req, res, next) => {
         req.session2.sessionBack = req.session;
     } else {
         req.session = new memcachedSession.Session(req);
+        req.session.cookie = new memcachedSession.Cookie({
+            domain: 'yohobuy.com',
+            httpOnly: false
+        });
         req.session = _.assign(req.session, req.session2.sessionBack);
     }
 
@@ -177,6 +182,6 @@ try {
 }
 
 // listener
-app.listen(config.port, function() {
+app.listen(config.port, function () {
     logger.info('yohobuy start');
 });