howto-maintain-git: discarding inactive topics

When a patch series happened to look interesting to the maintainer
but is not ready for 'next', it is applied on a topic branch and
merged to the 'seen' branch to keep an eye on it.  In an ideal
world, the participants give reviews and the original author
responds to the reviews, and such iterations may produce newer
versions of the patch series, and at some point, a concensus is
formed that the latest round is good enough for 'next'.  Then the
topic is merged to 'next' for inclusion in a future release.

In a much less ideal world we live in, however, a topic sometimes
get stalled.  The original author may not respond to hanging review
comments, may promise an update will be sent but does not manage to
do so, nobody talks about the topic on the list and nobody builds
upon it, etc.

Following the recent trend to document and give more transparency to
the decision making process, let's set a deadline to keep a topic
still alive, and actively discard those that are inactive for a long
period of time.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/howto/maintain-git.txt

@@ -67,7 +67,22 @@ the mailing list after each feature release is made:
    before getting merged to 'master'.
 
  - 'seen' branch is used to publish other proposed changes that do
-   not yet pass the criteria set for 'next' (see above).
+   not yet pass the criteria set for 'next' (see above), but there
+   is no promise that 'seen' will contain everything.  A topic that
+   had no reviewer reaction may not be picked up.
+
+   - A new topic will first get merged to 'seen', unless it is
+     trivially correct and clearly urgent, in which case it may be
+     directly merged to 'next' or even to 'master'.
+
+   - If a topic that was picked up to 'seen' becomes and stays
+     inactive for 3 calendar weeks without having seen a clear
+     consensus that it is good enough to be moved to 'next', the
+     topic may be discarded from 'seen'.  Interested parties are
+     still free to revive the topic.  For the purpose of this
+     guideline, the definition of being "inactive" is that nobody
+     has discussed the topic, no new iteration of the topic was
+     posted, and no responses to the review comments were given.
 
  - The tips of 'master' and 'maint' branches will not be rewound to
    allow people to build their own customization on top of them.