Fix cacthing exception object: a null exception is always caught.

tests/language/src/ExceptionTest.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.
 class ExceptionTest {
   static testMain() {
     int i = 0;
     try {
       throw "Hello";
     } catch (String s) {
       print(s);
       i += 10;
     }
 
     try {
       throw "bye";
     } catch (String s) {
       print(s);
       i += 10;
     }
     Expect.equals(20, i);
+
+    try {
+      throw null;
+    } catch (String s) {
+      // null exception object is caught here.

[hausner, 2012/02/21 21:47:48]

Actuall one more comment. Maybe have two catch clauses here and check that the
first one is executed.

[srdjan, 2012/02/21 21:53:52]

Done.

+    }
   }
 }
 
 main() {
   ExceptionTest.testMain();
 }