Fix wrong way of adding Error information in shutil.copytree.
diff --git a/Lib/shutil.py b/Lib/shutil.py
index 2d7a506..ef29ae2 100644
--- a/Lib/shutil.py
+++ b/Lib/shutil.py
@@ -236,7 +236,7 @@
             # Copying file access times may fail on Windows
             pass
         else:
-            errors.extend((src, dst, str(why)))
+            errors.append((src, dst, str(why)))
     if errors:
         raise Error(errors)