I want to gather some thoughts about this. Say you've written a patch series and are getting ready to send a -v2. If you set --in-reply-to=ask, it'll show you a list of emails you've recently sent, and their subject lines, and ask you to pick one to use the message ID from. It'll set the In-Reply-To header to your selection. I'd also like to add a custom header, X-Patch-Supersedes: <message ID>, with a similar behavior & purpose. Thoughts?
