Inconsistent behavior with country prefixes #485
Description
As far as I can tell from a bit of research (although I'm not 100% sure), the domestic form of both the Polish NIP and Romanian CF numbers are digits only, and a country prefix can be optionally added to the beginning when using it as an EU VAT number.
The NIP validator behaves like I would expect it to - the documentation says it should return "a compact, consistent representation of the number or code", and it does so - it always returns the domestic form of the number, without the country prefix. The CF validator, however, returns whatever it was passed - if you pass in a country-prefixed number, it outputs a country-prefixed number, and vice versa for a domestic number.
It's hard to rely on the output of the library when for some countries the format of the output depends on the format of the input. I don't know if this is just an issue of the Romanian validator, or a wider issue, but I think it warrants being checked out and corrected, so that the output is indeed compact and consistent.
Small side note: ro/cf.py is also missing checksum validation