Add executable to Options interface to get the name of the executable used to execute the script.

corelib/src/options.dart

-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// 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.
 
 // Dart core library.
 
 /**
  * The Options object allows accessing the arguments which have been passed to
  * the current isolate.
  */
 interface Options default RuntimeOptions {
   /**
    * A newly constructed Options object contains the arguments exactly as they
    * have been passed to the isolate.
    */
   Options();
 
   /**
    * Returns a list of arguments that have been passed to this isolate. Any
    * modifications to the list will be contained to the options object owning
    * this list.
    */
   List<String> get arguments();
 
   /**
+   * Returns the path of the executable used to run the script in this
+   * isolate.

[Ivan Posva, 2012/05/07 17:40:36]

Please comment what happens if the execution environment does not support this.
For example: "An empty string will be returned if the execution environment does
not provide access to this property."

Ditto for the other getters.

[Mads Ager (google), 2012/05/08 06:39:04]

Done.

[Anders Johnsen, 2012/05/09 07:16:43]

Any change we could change this to always be absolute? Or maybe, return a Path
object once available?

[Mads Ager (google), 2012/05/09 07:38:09]

This is in corelib so we shouldn't have dependencies on other libraries. On the
VM (which is the only embedder who has this) you can wrap this in a File object
and you are rolling. :-)

+   */
+  String get executable();
+
+  /**
    * Returns the path of the script being run in this isolate.
    */
   String get script();
 }