testing: make Eq(nan,<meh>) return False, same for _Inequality()

Not necessarily intended for a merge...
I am opposed to adding this to the *Than classes.  Note that, e.g. `LessThan(1, I)` does not simplify, returning a LessThan object, because complex numbers are not orderable with real numbers.  Similarly, I don't think that nan should be considered as orderable with real numbers.  False should not be used as a stand-in to indicate that the comparison makes no sense.