Update language.status and rewrite two tests

tests/language/constructor_return_test.dart

 // Copyright (c) 2011, 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.
 
 import "package:expect/expect.dart";
 
 // Dart spec 0.03, section 11.10 - generative constructors can only have return
 // statements in the form 'return;'.
 class A {
   int x;
   A(this.x) { return; } // 'return;' is equivalent to 'return this;'

[kustermann, 2013/08/30 11:12:44]

If 'return;' is equivalent to 'return this;', what is the difference between
'A()' and 'A.test1()' ?

[Søren Gjesse, 2013/08/30 13:40:02]

The comment is bogus, and I have removed it.

The spec says these two things:

It is a compile-time error if a return statement of the form return e; appears
in a generative constructor.

A return statement with no expression, return; is executed by executing the
statement return null;

+  A.test1(this.x) {
+    return this;  /// 01: compile-time error
+  }
+  A.test2(this.x) {
+    return null;  /// 02: compile-time error
+  }
   int foo(int y) => x + y;
 }
 
 main() {
   Expect.equals((new A(1)).foo(10), 11);
+  Expect.equals((new A.test1(1)).foo(10), 11);
+  Expect.equals((new A.test2(1)).foo(10), 11);
 }