graphlog: use '%' for other context in merge conflict This lets the user more easily find the commit that is involved in the conflict, such as the source of `hg update -m` or the commit being grafted by `hg graft`. Differential Revision: https://phab.mercurial-scm.org/D8043

{
    "conduit_uri": "https://phab.mercurial-scm.org/api",
    "phabricator.uri": "https://phab.mercurial-scm.org/",
    "repository.callsign": "HG",
    "arc.land.onto.default": "@",
    "base": "hg:.^"
}