.arcconfig

ui: install logger that sends debug.extensions messages to stderr

This will replace the custom log function introduced at d58958676b3c
"extensions: add detailed loading information."

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