Make "Nowhere" explicitly listable in torrc.

We already had the country code ?? indicating an unknown country, so all we
needed to do to make unknown countries excludable was to make the ?? code
discoverable.

src/or/geoip.c

@@ -200,6 +200,7 @@ geoip_load_file(const char *filename, or_options_t *options)
             sizeof(geoip_unresolved->countrycode));
     smartlist_add(geoip_countries, geoip_unresolved);
     country_idxplus1_by_lc_code = strmap_new();
+    strmap_set_lc(country_idxplus1_by_lc_code, "??", (void*)(1));
   }
   if (geoip_entries) {
     SMARTLIST_FOREACH(geoip_entries, geoip_entry_t *, e, tor_free(e));

src/or/routerlist.c

@@ -5335,6 +5335,10 @@ routerset_contains(const routerset_t *set, const tor_addr_t *addr,
     if (country < 0 && addr)
       country = geoip_get_country_by_ip(tor_addr_to_ipv4h(addr));
 
+    /* XXXX can we safely move this into geoip_get_country_by_ip? */
+    if (country < 0)
+      country = 0;
+
     if (country >= 0 && country < set->n_countries &&
         bitarray_is_set(set->countries, country))
       return 2;