Big merge from experimental to bleeding edge.

sdk/lib/core/strings.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.
 
 part of dart.core;
 
 abstract class Strings {
   /**
    * Joins all the given strings to create a new string.
    */
-  external static String join(List<String> strings, String separator);
+  external static String join(Iterable<String> strings, String separator);
 
   /**
    * Concatenates all the given strings to create a new string.
    */
-  external static String concatAll(List<String> strings);
+  external static String concatAll(Iterable<String> strings);
 }