error: Fix super calls for SMTPAuthenticationError, etc.

Fix copy/paste errors where super() calls used the wrong class name
(it should match the class in which the method is defined) for:

* SMTPAuthenticationError.__init__
* ProcessingError.__init__
* OPMLReadError.__init__

Reported-by: Matt Bordignon <matthew@bordignons.net>
Signed-off-by: W. Trevor King <wking@tremily.us>