www: sort all /$INBOX/ topics by Received: timestamp
Our previous pinning prevention only worked to prevent older
(non-most-recent) topics from being pinned to the landing page,
but not the most recent window of messages.
We still sort messages within threads by Date: because that
makes git-send-email patchsets display more nicely, but we
don't want recent topics pinned due to future Date: headers.
I nearly switched sort_ds() back to sorting by Received: until
I looked back on commit
8e52e5fdea416d6fda0b8d301144af0c043a5a76
(use both Date: and Received: times, 2018-03-21) and was reminded
git-send-email relies on Date: for large series, so I added a
note about it for sort_ds().
Reported-by: Kyle Meyer <kyle@kyleam.com>
Tested-by: Kyle Meyer <kyle@kyleam.com>
Link: https://public-inbox.org/meta/87edr5gx63.fsf@kyleam.com/