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 =  * ;
             Stopwatch watch = new Stopwatch();

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

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

             String str = "abcdefghijklmnopqrstuvwxyz中华人民共和国";
             watch = Stopwatch.StartNew();
             for (int i = ; 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