Be a little bit more robust about temporary connection errors.
Be a little bit more robust about temporary connection errors.

We should catch a slightly broader range of exceptions when attempting
to make a connection and/or login, and avoid quitting except where
recovery is exceptionally unlikely.

So, an `imaplib.IMAP4.error` indicates truly exceptional circumstances
and still causes us to quit, whereas an `imaplib.IMAP4.abort` indicates
well-formed errors due to connection woes or login failure. We now
don't quit in the latter case.

We catch almost anything thrown by `smtplib` however, as it doesn't have
such a clear distinction between programming errors and connection
errors. It's fair to assume, however, that smtplib doesn't contain too
many of the former any more.

nickstenning/imaprelay