Merge branch 'ga/send-email-sendmail-cmd'

"git send-email" learned the "--sendmail-cmd" command line option
and the "sendemail.sendmailCmd" configuration variable, which is a
more sensible approach than the current way of repurposing the
"smtp-server" that is meant to name the server to instead name the
command to talk to the server.

* ga/send-email-sendmail-cmd:
  git-send-email: add option to specify sendmail command

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

diff --cc t/t9001-send-email.sh
Simple merge