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

utils/pub/command_lish.dart

Index: utils/pub/command_lish.dart
diff --git a/utils/pub/command_lish.dart b/utils/pub/command_lish.dart
index 84afdc03a1e25e6f38a76a43a245d8d22e588e3f..2de62a8ad1f1f1fca04d74551351946fd6b0ed33 100644
--- a/utils/pub/command_lish.dart
+++ b/utils/pub/command_lish.dart
@@ -147,7 +147,7 @@ class LishCommand extends PubCommand {
 
       return listDir(rootDir, recursive: true).then((entries) {
         return entries
-            .where(fileExists) // Skip directories.
+            .where(fileExists) // Skip directories and broken symlinks.
             .map((entry) => path.relative(entry, from: rootDir));
       });
     }).then((files) => files.where(_shouldPublish).toList());