debuginstall: use codecs.lookup() to detect invalid encoding
encoding.fromlocal() never tries to decode an ascii string since
853574db5b12,
and there's no universal non-ascii string which can be decoded as any valid
character set.
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}