changelog: also monitor `00changelog.n` when applicable (
issue6554)
This let the locarepo's file cache detect outdated nodemap docket and reload the
changelog after `localrepo.invalidate` when applicable.
Differential Revision: https://phab.mercurial-scm.org/D11482
local test passed
addgroupcopy test passed
clone test passed
lowlevelcopy test passed
slicing test passed
issnapshot test passed
findsnapshot test passed