Subject: 27.1; indicate which articles we have piped

From: 積丹尼 Dan Jacobson <[email-masked]>
Date: Thu, 19 Aug 2021 19:54:07 +0800

| runs the command gnus-summary-pipe-output

it is great, but unlike articles we save,
there is no mark, however temporary,
showing which articles we piped,
vs. which articles we didn't yet pipe.