revlog: move the "index header" struct inside revlog.utils.constants
The struct was previous called "version", but this is actually "version" +
"flags". So header seems like a better name.
The move to the `constants` module has the same motivation as the INDEX_ENTRY_V#
ones.
Differential Revision: https://phab.mercurial-scm.org/D10306
# __init__.py - Startup and module loading logic for Mercurial.
#
# Copyright 2015 Gregory Szorc <gregory.szorc@gmail.com>
#
# 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
# Allow 'from mercurial import demandimport' to keep working.
import hgdemandimport
demandimport = hgdemandimport