Merge branch 'jw/send-email-no-auth'

"git send-email" learned to disable SMTP authentication via the
"--smtp-auth=none" option, even when the smtp username is given
(which turns the authentication on by default).

* jw/send-email-no-auth:
send-email: explicitly disable authentication

diff --cc Documentation/git-send-email.txt
Simple merge

diff --cc git-send-email.perl
Simple merge