Clean up the semantics of io.dart operations w.r.t. symlinks.

utils/pub/source.dart

Index: utils/pub/source.dart
diff --git a/utils/pub/source.dart b/utils/pub/source.dart
index 60d455b6164305b544984d0635a565bd624015fc..118096710e0c5f11267d7f94bc473bee9766f0a2 100644
--- a/utils/pub/source.dart
+++ b/utils/pub/source.dart
@@ -119,7 +119,7 @@ abstract class Source {
         if (!isCorrupted) return true;
 
         // Busted, so wipe out the package and reinstall.
-        deleteDir(packageDir);
+        deleteEntry(packageDir);
         return false;
       });
     }).then((isInstalled) {