Make the Mailbox objects support iteration -- they already had the

appropriate next() method, and this is what people really want to do with
these objects in practice.

Lib/mailbox.py

@@ -14,6 +14,9 @@ class _Mailbox:
         self.seekp = 0
         self.factory = factory
 
+    def __iter__(self):
+        return self
+
     def next(self):
         while 1:
             self.fp.seek(self.seekp)
@@ -191,6 +194,9 @@ class MHMailbox:
         self.boxes = map(str, list)
         self.factory = factory
 
+    def __iter__(self):
+        return self
+
     def next(self):
         if not self.boxes:
             return None
@@ -219,6 +225,9 @@ class Maildir:
 
         self.boxes = boxes
 
+    def __iter__(self):
+        return self
+
     def next(self):
         if not self.boxes:
             return None