walk(): Fix docstring; traversal is depth-first.  Closes mimelib bug
#477864.
diff --git a/Lib/email/Message.py b/Lib/email/Message.py
index 6f0db85..7216e38 100644
--- a/Lib/email/Message.py
+++ b/Lib/email/Message.py
@@ -423,7 +423,7 @@
     def walk(self):
         """Walk over the message tree, yielding each subpart.
 
-        The walk is performed in breadth-first order.  This method is a
+        The walk is performed in depth-first order.  This method is a
         generator.
         """
         yield self