#11686: add missing entries to email __all__ lists.

Original patch by Steffen Daode Nurpmeso
diff --git a/Lib/email/generator.py b/Lib/email/generator.py
index 430ee73..04c0210 100644
--- a/Lib/email/generator.py
+++ b/Lib/email/generator.py
@@ -4,7 +4,7 @@
 
 """Classes to generate plain text from a message object tree."""
 
-__all__ = ['Generator', 'DecodedGenerator']
+__all__ = ['Generator', 'DecodedGenerator', 'BytesGenerator']
 
 import re
 import sys