keepalive: implement _close_conn() so closes are known
Keepalives were not working on Python 3 because
http.client.HTTPResponse was refactored to call _close_conn()
instead of close(). Our custom close() is what returns inactive
connections to the available state.
We better support Python 3 by implementing a _close_conn().
Differential Revision: https://phab.mercurial-scm.org/D5720
running: init test1
result: 0
running: add foo
result: 0
running: commit -m commit1 -d 2000-01-01 foo
result: 0
running: commit -m commit2 -d 2000-01-02 foo
result: 0
running: log -r 0
changeset: 0:0e4634943879
user: test
date: Sat Jan 01 00:00:00 2000 +0000
summary: commit1
result: 0
running: log -r tip
changeset: 1:45589e459b2e
tag: tip
user: test
date: Sun Jan 02 00:00:00 2000 +0000
summary: commit2
result: 0