fix bug in isolate code, reenable isolate tests

lib/isolate/frog/isolateimpl.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.
 
 /**
  * Concepts used here:
  *
  * "manager" - A manager contains one or more isolates, schedules their
  * execution, and performs other plumbing on their behalf.  The isolate
  * present at the creation of the manager is designated as its "root isolate".
@@ skipping 153 matching lines @@
     initGlobals();
   }
 
   // these are filled lazily the first time the isolate starts running.
   void initGlobals() native @'$initGlobals(this);';
 
   /**
    * Run [code] in the context of the isolate represented by [this]. Note this
    * is called from JavaScript (see $wrap_call in corejs.dart).
    */
-  void eval(Function code) {
+  Dynamic eval(Function code) {
     var old = _globalState.currentContext;
     _globalState.currentContext = this;
     this._setGlobals();
     var result = null;
     try {
       result = code();
     } finally {
       _globalState.currentContext = old;
       if (old != null) old._setGlobals();
     }
@@ skipping 490 matching lines @@
       'command': 'start2',
       'id': workerId,
       // Note: we serialize replyPort twice because the child worker needs to
       // first deserialize the worker id, before it can correctly deserialize
       // the port (port deserialization is sensitive to what is the current
       // workerId).
       'replyTo': _serializeMessage(replyPort),
       'functionName': functionName }));
   }
 }