cmdutil: use internal separators when building the terse list
Status uses internal separators, so this is more correct. See c974320d20b9 and
362096cfdb1f. A utility method is still needed, so that the paths starting with
'/' aren't created when `self.path` is empty.
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}