revlog: pass around the `rev` we deal with when packing/unpacking entry
This will help code to compute some flag on the fly.
Differential Revision: https://phab.mercurial-scm.org/D10664
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}