Merge branch 'bg/send-email-smtpdomain'

* bg/send-email-smtpdomain:
send-email: Cleanup smtp-domain and add config
Document send-email --smtp-domain
send-email: Don't use FQDNs without a '.'
send-email: Cleanup { style

diff --cc Documentation/config.txt
Simple merge

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

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