rhg: Silently ignore missing files in config %include
… instead of aborting with an error message.
This is what Python-based hg does.
Differential Revision: https://phab.mercurial-scm.org/D10141
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}