.arcconfig

git: adapt to some recent dirstate API changes

There are still old methods like add() and drop().  I don't see anything that
looks equivalent, so there's likely more work to do.  But this allows diff and
commit to work again on the simple webpage repo for thg.

Differential Revision: https://phab.mercurial-scm.org/D12567

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