Don't use normalized types in type errors

[zuiderkwast]

From this comment by @Zalastax:

[...] At least some types get normalized and their normalized form gets reported in the error. E.g.

-spec f(char()) -> ok.
f(C) -> C.

The variable 'C' on line 5 has type 0..1114111 but is expected to have type ok

We can test this now, using the return_errors option.