Disallow double in case clauses and const map literal keys

tests/language/switch_int_double_test.dart

-// Copyright (c) 2013, 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 reporting a compile-time error if case expressions do not all have
-// the same type.
-
-import "package:expect/expect.dart";
-
-void main() {
-  Expect.equals(100, test(1.0));
-  Expect.equals(75, test(0.75));
-  Expect.equals(null, test(0.5));
-}
-
-int test(num ratio) {
-  switch (ratio) {
-    case 0.75:
-      return 75;
-    case 1.0:
-      return 100;
-    case 2:       /// 01: compile-time error
-      return 200; /// 01: continued
-    case 'foo':   /// 02: compile-time error
-      return 400; /// 02: continued
-  }
-}