Alpine is apparently stricter than other clients I've tried
w.r.t. using CRLF for headers. So do the same thing we do for
bodies to ensure we only emit CRLFs and no bare LFs.
Reported-by: Wang Kang <i@scateu.me>
https://public-inbox.org/meta/alpine.DEB.2.21.99.1901161043430.29788@la.scateu.me/