使用ToUpperInvariant避免使用ToUpper

ToUpperInvariant使用不依赖于区域性进行转换，而ToUpper则使用了当前线程的CultureInfo，进行转换，所以性能会有所影响，以下为测试：

        [Test]
        public void TestInvariant()
        {
            Int32 count = 1000 * 1000;
            Stopwatch watch = new Stopwatch();

            String str = "abcdefghijklmnopqrstuvwxyz中华人民共和国";
            watch = Stopwatch.StartNew();
            for (int i = 0; i < count; i++)
            {
                str.ToUpperInvariant();
            }
            Console.WriteLine("ToUpperInvariant:{0}", watch.Elapsed.ToString());
        }

        [Test]
        public void TestNoInvariant()
        {
            Int32 count = 1000 * 1000;
            Stopwatch watch = new Stopwatch();

            String str = "abcdefghijklmnopqrstuvwxyz中华人民共和国";
            watch = Stopwatch.StartNew();
            for (int i = 0; i < count; i++)
            {
                str.ToUpper();
            }
            Console.WriteLine("ToUpper:{0}", watch.Elapsed.ToString());
        }

ToUpperInvariant:00:00:00.2980660

ToUpper:00:00:00.3281423

如果 确认当前的比较和区域性无关的话，推荐使用ToUppperInvariant