revlog: move the details of revlog "v2" index inside revlog.utils.constants
the revlog module is quite large and this kind of format information would handy
for other module. So let us start to gather this information about the format in
a more appropriate place.
We update various reference to this information to use the new "source of truth"
in the process.
Differential Revision: https://phab.mercurial-scm.org/D10305
Issue1678: IndexError when pushing
setting up base repo
$ hg init a
$ cd a
$ touch a
$ hg ci -Am a
adding a
$ cd ..
cloning base repo
$ hg clone a b
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd b
setting up cset to push
$ hg up null
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ touch a
different msg so we get a clog new entry
$ hg ci -Am b
adding a
created new head
pushing
$ hg push -f ../a
pushing to ../a
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 0 changes to 0 files (+1 heads)
$ cd ..