Equivalence for errors

[daemontus]

Right now, all errors seem to implement PartialEq, but mostly it is derived, only for the bindings errors it needs to be implemented explicitly based on the enum discriminant. I'm not quite sure how to interpret this. What are the equality criteria for the derived case? Is it the data in the error or just discriminant? If it's the data, shouldn't we try to have something like that for the Python errors as well? If it's just the discriminant, this should probably be documented somewhere?