Make VersionSolver source- and description-aware.

utils/pub/entrypoint.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.
 
 #library('entrypoint');
 
 #import('io.dart');
 #import('package.dart');
 #import('system_cache.dart');
 #import('version.dart');
@@ skipping 122 matching lines @@
   /**
    * Given [ref], which ambiguously identifies a dependent package, selects an
    * appropriate precise package to use when this is the entrypoint. In other
    * words, given a loose refence like "foo >= 2.0", figures out what concrete
    * package we should use starting from this entrypoint.
    */
   Future<PackageId> resolve(PackageRef ref) {
     // TODO(rnystrom): This should use the lockfile to select the right version
     // once that's implemented. If the lockfile doesn't exist, it should
     // generate it. In the meantime, here's a dumb implementation:
-    return new Future.immediate(
-        new PackageId(ref.source, ref.constraint, ref.description));
+    return new Future.immediate(ref.atVersion(ref.constraint));
   }
 }