Merge branch 'mh/maint-fix-send-email-threaded' into mh/fix-send-email-threaded

* mh/maint-fix-send-email-threaded: doc/send-email: clarify the behavior of --in-reply-to with --no-thread send-email: fix non-threaded mails add a test for git-send-email for non-threaded mails Conflicts: git-send-email.perl t/t9001-send-email.sh