Make unittest follow the new package layout.

pkg/unittest/lib/src/interfaces.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.
 
 // To decouple the reporting of errors, and allow for extensibility of
 // matchers, we make use of some interfaces.
 
 /**
  * The ErrorFormatter type is used for functions that
  * can be used to build up error reports upon [expect] failures.
@@ skipping 79 matching lines @@
    * the [reason] (argument from [expect]), some additonal [matchState]
    * generated by the [matcher], and a verbose flag which controls in
    * some cases how much [matchState] information is used. It will use
    * these to create a detailed error message (typically by calling
    * an [ErrorFormatter]) and then call [fail] with this message.
    */
   void failMatch(actual, Matcher matcher, String reason,
                  MatchState matchState, bool verbose);
 }