AFN 加Header

　　AFHTTPSessionManager * manager = [AFHTTPSessionManager manager];
    manager.responseSerializer.acceptableContentTypes = [NSSet setWithObjects:@"application/json", @"text/json",@"text/javascript",@"text/html",nil];
    manager.requestSerializer = [AFHTTPRequestSerializer serializer];
    manager.responseSerializer = [AFHTTPResponseSerializer serializer];
    [manager.requestSerializer setValue:[UserData getSessionId] forHTTPHeaderField:@"JSESSIONID"];//加入了header头，然后就可以去请求了。