Handle shared path dependencies.

utils/pub/path_source.dart

Index: utils/pub/path_source.dart
diff --git a/utils/pub/path_source.dart b/utils/pub/path_source.dart
index 31ea9fb75157abafeb77474340ffc1a47600c11f..f9b2991306ffa6ddc6dd31989fce3b83d32e4226 100644
--- a/utils/pub/path_source.dart
+++ b/utils/pub/path_source.dart
@@ -9,6 +9,8 @@ import 'dart:io';
 
 import '../../pkg/pathos/lib/path.dart' as path;
 
+import 'log.dart' as log;
+
 import 'io.dart';
 import 'package.dart';
 import 'pubspec.dart';
@@ -30,6 +32,14 @@ class PathSource extends Source {
     });
   }
 
+  bool descriptionsEqual(description1, description2) {
+    // TODO(rnystrom): Traverse symlinks and compare real paths?

[nweiz, 2013/02/25 22:08:46]

I'm leaning towards yes.

[Bob Nystrom, 2013/02/25 22:50:26]

Done.

+    var path1 = path.normalize(description1["path"]);
+    var path2 = path.normalize(description2["path"]);
+    return path1 == path2 &&
+        description1["relative"] == description2["relative"];

[nweiz, 2013/02/25 22:08:46]

I don't think this is correct. If both paths resolve to the same location,
they're always pointing to the same package, regardless if one is relative and
the other isn't.

[Bob Nystrom, 2013/02/25 22:50:26]

Done.

+  }
+
   Future<bool> install(PackageId id, String destination) {
     return defer(() {
       try {
@@ -44,7 +54,7 @@ class PathSource extends Source {
   }
 
   /// Parses a path dependency. This takes in a path string and returns a map.
-  /// The "path" key will be the original path but resolves relative to the
+  /// The "path" key will be the original path but resolved relative to the
   /// containing path. The "relative" key will be `true` if the original path
   /// was relative.
   ///