Update unittest to new package layout.

pkg/unittest/lib/src/numeric_matchers.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.
 
 /**
  * Returns a matcher which matches if the match argument is greater
  * than the given [value].
  */
 Matcher greaterThan(value) =>
   new _OrderingComparison(value, false, false, true, 'a value greater than');
@@ skipping 209 matching lines @@
       return mismatchDescription.
           addDescriptionOf(item).
           add(' not numeric');
     } else {
       return super.describeMismatch(item, mismatchDescription,
           matchState, verbose);
     }
   }
 }