重载了一个方法：
public class RepeatDictionaryComparer : IEqualityComparer<string>
{
public bool Equals(string x, string y)
{
return x != y;
}
public int GetHashCode(string obj)
{
return obj.GetHashCode();
}
}
调用：
Dictionary<string, string> _dic = new Dictionary<string, string>(new RepeatDictionaryComparer());
这样重复的键也可以添加了