It's not enough to place header after first newline, since this might break
multiline rfc0822 folded long header lines. Those are difined as CRLF followed
by white space. Instead we'll search for two successive CRLF sequences which
mark end of mail headers and place our header just before that.
Signed-off-by: Vladimir Marek <vlmarek@volny.cz>
Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>
86e9c7442b