Re: [RFH] Mention of 1.7.0 transition plans in Release Notes to 1.6.6

Nanako Shiraishi [off-list ref] writes:

Subject: prepare send-email for smoother change of --chain-reply-to default

Give a warning message when send-email uses chain-reply-to to thread the
messages because of the current default, not because the user explicitly
asked to, either from the command line or from the configuration.

This way, by the time 1.7.0 switches the default, everybody will be ready.

Signed-off-by: Nanako Shiraishi <redacted>
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Looks good.