revlogv2: use a unique filename for index
Having a unique index will allow for ambiguity less rewriting of revlog content,
something useful to clarify handling of some operation like censoring or
stripping.
Differential Revision: https://phab.mercurial-scm.org/D10771
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}