xor can make internal integers negative

[anmolitor]

Here is an example:

> minusOne = Int64.fromInt32s 0 -1
Int64 0 4294967295 : Int64.Int64
> xored = Int64.xor (Int64.fromInt 0) minusOne
Int64 0 -1 : Int64.Int64

The issue is that other operations do not work as expected anymore - comparing does not return EQ and == returns False.

[anmolitor]

Workaround: Int64.complement >> Int64.complement after xor.