Contract violating Equals

On floating point numbers `==` behaves in a way that violates the contract of `Equals`. So the behavior differs between `==` and `Equals` for such types.
One property `Equals` needs to have is that for every `a` : `a.Equals(a)`.

`NaN==NaN`  =>  `false` but `NaN.Equals(NaN)` => true

you need to mirror that property in your structs.
