send-email and in-reply-to = n

Can we throw up a big warning or just outright fail if someone types
'n' or 'y' and hits enter for the in-reply-to question in
git-send-email? I saw a git-send-email sent patch with an In-Reply-To
header containing n on lkml today and it makes threading in my mail
client get confused.

https://lkml.org/lkml/headers/2012/8/13/503