为什么float.NaN！= double.NaN？
而float.PositiveInfinity == double.PositiveInfinity和float.NegativeInfinity == double.NegativeInfinity相等。
例：
bool PosInfinity = (float.PositiveInfinity == double.PositiveInfinity); //true bool NegInfinity = (float.NegativeInfinity == double.NegativeInfinity); //true bool isNanEqual = (float.NaN == double.NaN); //false,WHY?
