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

utils/pub/pub.dart

Index: utils/pub/pub.dart
diff --git a/utils/pub/pub.dart b/utils/pub/pub.dart
index 1c05c45b977acf5a48f87bc588ea6d9741b4a09c..c2fb8f9b0fb45837d5743c0dc04726491830605d 100644
--- a/utils/pub/pub.dart
+++ b/utils/pub/pub.dart
@@ -258,6 +258,8 @@ abstract class PubCommand {
       if (globalOptions['trace'] && trace != null) {
         log.error(trace);
         log.dumpTranscript();
+      } else {
+        log.fine(trace);
       }
 
       exit(_chooseExitCode(error));