Correct file names for tests in tests/language.

tests/language/double_int_to_string_test.dart

+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+// Test basic integer operations.
+
+main() {
+  Expect.equals("0.0", (0.0).toString());
+  Expect.equals("9.0", (9.0).toString());
+  Expect.equals("90.0", (90.0).toString());
+  Expect.equals("111111111111111110000.0",
+                (111111111111111111111.0).toString());
+  Expect.equals("-9.0", (-9.0).toString());
+  Expect.equals("-90.0", (-90.0).toString());
+  Expect.equals("-111111111111111110000.0",
+                (-111111111111111111111.0).toString());
+  Expect.equals("1000.0", (1000.0).toString());
+  Expect.equals("1000000000000000100.0", (1000000000000000128.0).toString());
+}