#2118: Make SMTPException a subclass of IOError.

Initial patch by Ned Jackson Lovely.
diff --git a/Doc/library/smtplib.rst b/Doc/library/smtplib.rst
index 9593dea..04036dc 100644
--- a/Doc/library/smtplib.rst
+++ b/Doc/library/smtplib.rst
@@ -103,8 +103,8 @@
 
 .. exception:: SMTPException
 
-   The base exception class for all the other excpetions provided by this
-   module.
+   Subclass of :exc:`IOError` that is the base exception class for all
+   the other excpetions provided by this module.
 
 
 .. exception:: SMTPServerDisconnected