TINSEL: Fix #3422433 ("DW2: US version uses UK graphics")

According to dreammaster it should be enough to add cases for the
US version in these two functions, but unfortunately he can't test
it himself. I guess I should try to find the time to play through
the game, but right now there's an annoying DW2 regression from
commit d5690e0. See GitHub commit note for details.

NEWS

@@ -61,6 +61,8 @@ For a more comprehensive changelog of the latest experimental code, see:
 
  Tinsel:
    - Fixed a regression that made Discworld uncompletable.
+   - The US version of Discworld II now shows the correct title screen and
+     language flag.
 
  SAGA:
    - Fixed a regression in Inherit the Earth's dragon walk code which

engines/tinsel/config.cpp

@@ -76,6 +76,9 @@ void Config::writeToDisk() {
 		case TXT_ITALIAN:
 			lang = Common::IT_ITA;
 			break;
+		case TXT_US:
+			lang = Common::EN_USA;
+			break;
 		default:
 			lang = Common::EN_ANY;
 		}
@@ -132,6 +135,9 @@ void Config::readFromDisk() {
 	case Common::IT_ITA:
 		_language = TXT_ITALIAN;
 		break;
+	case Common::EN_USA:
+		_language = TXT_US;
+		break;
 	default:
 		_language = TXT_ENGLISH;
 	}