Add login() method and SMTPAuthenticationError exception.  SF patch #460112 by Gerhard Haering.
Add login() method and SMTPAuthenticationError exception.  SF patch
#460112 by Gerhard Haering.

(With slight layout changes to conform to docstrings guidelines and to
prevent a line longer than 78 characters.  Also fixed some docstrings
that Gerhard didn't touch.)

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator