tests/test-inotify-lookup.t

clfilter: handle non contiguous iteration in `revlov.headrevs`

This prepares changelog level filtering.  We can't assume that any revision can
be heads because filtered revisions need to be excluded.

New algorithm:
- All revisions now start as "non heads",
- every revision we iterate over is made candidate head,
- parents of iterated revisions are definitely not head.

Filtered revisions are never iterated over and never considered as candidate
head.

  $ "$TESTDIR/hghave" inotify || exit 80
  $ hg init
  $ echo "[extensions]" > .hg/hgrc
  $ echo "inotify=" >> .hg/hgrc
  $ hg inserve -d --pid-file .hg/inotify.pid
  $ echo a > a
  $ hg ci -Aqm0
  $ hg co -q null
  $ hg co -q
  $ hg st
  $ cat a
  a
  $ kill `cat .hg/inotify.pid`