Merge branch 'rv/sendemail-tocmd-in-config-and-completion'

Teach "sendemail.tocmd" to places that know about "sendemail.to",
like documentation and shell completion (in contrib/).

* rv/sendemail-tocmd-in-config-and-completion:
completion: add git config sendemail.tocmd
Documentation/config: add sendemail.tocmd to list preceding "See git-send-email(1)"

diff --cc Documentation/config.txt
Simple merge

diff --cc contrib/completion/git-completion.bash
Simple merge