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

* mh/fix-send-email-threaded: send-email: fix a typo in a comment send-email: fix threaded mails without chain-reply-to add a test for git-send-email for threaded mails without chain-reply-to 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