revlogutils: move the NodeMap class in a dedicated nodemap module
We will introduce more nodemap related code, so it make sense to move the
existing code in that module first.
Differential Revision: https://phab.mercurial-scm.org/D7809
# mercurial.revlogutils -- basic utilities for revlog
#
# Copyright 2019 Pierre-Yves David <pierre-yves.david@octobus.net>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.
from __future__ import absolute_import