[PATCH 0 of 4 RFC] smtp: verify the certificate of the SMTP server for STARTTLS/SMTPS

[FUJIWARA Katsunori]

This patch series verifies the certificate of SMTP server for
STARTTLS/SMTPS.

Please comment especially about configuration for verification and
default value of it: I'm still wondering between security, backward
compatibility and similarity to other remote commands(push/pull with
--insecure).

BTW, "smtplib.SSLFakeFile" is available with Python 2.x but not with
3.x. Should I put some code to make it portable between 2.x and 3.x ?
(even though it is not yet useful now and for a while)