Implement and apply PEP 322, reverse iteration
diff --git a/Lib/rfc822.py b/Lib/rfc822.py
index 4f69b22..9a52a90 100644
--- a/Lib/rfc822.py
+++ b/Lib/rfc822.py
@@ -421,8 +421,7 @@
                 hit = 0
             if hit:
                 list.append(i)
-        list.reverse()
-        for i in list:
+        for i in reversed(list):
             del self.headers[i]
 
     def setdefault(self, name, default=""):