tests: splitting test-gendoc.t into per file tests Localizers can now run test-gendoc-$LOCALE.t instead of test-gendoc.t. After this change, test-gendoc.t only checks whether there is *some* localization for the expected set of languages and no others. Whenever a locale i18n/$LOCALE.po is added, someone needs to add test-gendoc-$LOCALE.t