.arcconfig

rhg: Sort config files when adding a directory

For example in `/etc/mercurial/hgrc.d/` or with `HGRCPATH=some-directory`.
Previously files where parsed in the order returned by the filesystem,
which is undefined. But order is significant when multiple files
define the same configuration key: the "last" one wins.

Differential Revision: https://phab.mercurial-scm.org/D10111

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