The similar list will be calculated only for
error.UnknownIdentifier. It was then printed only if `inst.location
is None`, which is true for that exception type, but it's an indirect
condition to rely on.
Also, it looked from the code like it could both report similarities
and print a hint. That would be a little awkward because the
similarity report looks similar to the hint (both are printed within
parentheses). I also added a elif to clarify that. I plan to
refactor this more coming patches so the similarity report actually is
a hint.