phabricator: use .arcconfig for `phabricator.url` if not set locally This setting is also per repo; see the previous commit for details. The existing `conduit_uri` setting is the previous name of `phabricator.uri`[1] and while it could easily be queried before the latter for compatibility, the config in this repo has '/api' appended. That's already done in `callconduit()`, which would clearly end up giving the wrong result. It looks like the path of the URL is now ignored in user configs[2], so add the modern setting without it to this repo's .arcconfig. Sadly, we still need to have contributors configure `auth.hg.phabtoken` (and therefore `auth.hg.prefix` to link it to `phabricator.url`) in order to submit patches, but at least now it's localized to a single section. [1] https://secure.phabricator.com/book/phabricator/article/arcanist_new_project/ [2] https://github.com/phacility/arcanist/blob/cc850163f30c4697e925df0d6212469679600a2c/scripts/arcanist.php#L271 Differential Revision: https://phab.mercurial-scm.org/D7935