Bug #1030125:  rfc822 __iter__ problem

Add iteration support to the Message class.
diff --git a/Lib/test/test_rfc822.py b/Lib/test/test_rfc822.py
index 491bc8a..0d9f28a 100644
--- a/Lib/test/test_rfc822.py
+++ b/Lib/test/test_rfc822.py
@@ -176,6 +176,17 @@
             'foo',
             [('', 'guido@[132.151.1.21]')])
 
+    def test_iter(self):
+        m = rfc822.Message(StringIO(
+            'Date:    Wed, 13 Jan 1999 23:57:35 -0500\n'
+            'From:    Guido van Rossum <guido@CNRI.Reston.VA.US>\n'
+            'To:      "Guido van\n'
+            '\t : Rossum" <guido@python.org>\n'
+            'Subject: test2\n'
+            '\n'
+            'test2\n' ))
+        self.assertEqual(sorted(m), ['date', 'from', 'subject', 'to'])
+
     def test_rfc2822_phrases(self):
         # RFC 2822 (the update to RFC 822) specifies that dots in phrases are
         # obsolete syntax, which conforming programs MUST recognize but NEVER