Implement correct scoping rules for variables.

tests/language/scope_variable2_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.
-// Dart test for testing binary operations.
-// VMOptions=--verify_implements  --check-function-fingerprints
 
-class BootstrapTest {
+var x = 0;
 
-  static testMain() {
-    var obj = new Object();
-
-    return obj;
+f(y) {
+  var z = x;  /// 01: compile-time error
+  if (y) {
+    x = x + 1;  /// 02: compile-time error
+    print(x);  /// 03: compile-time error
   }
-
+  var x
+    = x++  /// 04: compile-time error
+  ;
+  print(x);
 }
 
 main() {
-  BootstrapTest.testMain();
+  f(true);
 }