howto-maintain-git: discarding inactive topics

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>