fixes #201, add support for custom URL mapping

lib/src/dependency_graph.dart

 // Copyright (c) 2015, 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.
 
 /// Tracks the shape of the import/export graph and dependencies between files.
 library dev_compiler.src.dependency_graph;
 
 import 'dart:collection' show HashSet, HashMap;
 
 import 'package:analyzer/analyzer.dart' show parseDirectives;
@@ skipping 283 matching lines @@
 
         var directiveUri = (d as UriBasedDirective).uri;
 
         // `dart:core` and other similar URLs only contain a name, but it is
         // meant to be a folder when resolving relative paths from it.
         var targetUri = uri.scheme == 'dart' && uri.pathSegments.length == 1
             ? Uri.parse('$uri/').resolve(directiveUri.stringValue)
             : uri.resolve(directiveUri.stringValue);
         var target =
             ParseDartTask.resolveDirective(graph._context, _source, d, null);
-        if (target != null) {
-          if (targetUri != target.uri) print(">> ${target.uri} $targetUri");
-        }
         var node = graph.nodes.putIfAbsent(
             targetUri, () => new DartSourceNode(graph, targetUri, target));
         //var node = graph.nodeFromUri(targetUri);
         if (node._source == null || !node._source.exists()) {
           _reportError(graph, 'File $targetUri not found', unit, d);
         }
 
         if (d is ImportDirective) {
           newImports.add(node);
         } else if (d is ExportDirective) {
@@ skipping 214 matching lines @@
   'dart._interceptors',
   'dart._native_typed_data',
   */
 ];
 
 /// Runtime files added to applications when running in server mode.
 final runtimeFilesForServerMode = new List<String>.from(defaultRuntimeFiles)
   ..addAll(const ['messages_widget.js', 'messages.css']);
 
 final _log = new Logger('dev_compiler.dependency_graph');