Revert "Use relative URIs for core library part-of statements."

sdk/lib/core/num.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.
 
-part of "core.dart";
+part of dart.core;
 
 /**
  * An integer or floating-point number.
  *
  * It is a compile-time error for any type other than [int] or [double]
  * to attempt to extend or implement num.
  */
 abstract class num implements Comparable<num> {
   /**
    * Test whether this value is numerically equal to `other`.
@@ skipping 455 matching lines @@
     result = double.parse(source, _returnDoubleNull);
     if (result != null) return result;
     if (onError == null) throw new FormatException(input);
     return onError(input);
   }
 
   /** Helper functions for [parse]. */
   static int _returnIntNull(String _) => null;
   static double _returnDoubleNull(String _) => null;
 }