Add an ArgResults.original getter.

pkg/args/test/args_test.dart

Index: pkg/args/test/args_test.dart
diff --git a/pkg/args/test/args_test.dart b/pkg/args/test/args_test.dart
index 6792c95e68a5b67563c08ef28334287207b937f1..77c23c329311e5ac308400b03def18da6767226c 100644
--- a/pkg/args/test/args_test.dart
+++ b/pkg/args/test/args_test.dart
@@ -228,6 +228,14 @@ void main() {
       expect(() => results.rest.add('oops'), throwsUnsupportedError);
     });
 
+    test('.arguments returns the original argument list', () {
+      var parser = new ArgParser();
+      parser.addFlag('foo');
+
+      var results = parser.parse(['--foo']);
+      expect(results.arguments, equals(['--foo']));
+    });
+
     group('.wasParsed()', () {
       test('throws if the name is not an option', () {
         var results = new ArgParser().parse([]);