Merge branch 'al/send-email-auto-cte-fixup'

"git send-email --transfer-encoding=..." in recent versions of Git
sometimes produced an empty "Content-Transfer-Encoding:" header,
which has been corrected.

* al/send-email-auto-cte-fixup:
send-email: avoid empty transfer encoding header

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

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