.arcconfig

i18n: format warning of hggettext in standard compiler error style

Now, hggettext specific warning messages are formatted in:

    FILENAME:LINENO:MESSAGE

This allows editors to jump into corresponded line easily.

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