LCNAF/LCSH should rewrite -781 URIs to base

[azaroth42]

... to prevent missing links from other systems that might still use them. This could be done in mapper.fix_identifier() which is called from split_uri() which is in turn used by canonicalize()

e.g. a reference to http://id.loc.gov/authorities/names/n80046090-781 should instead be to n80046090 by being "fixed"