.arcconfig

match: test for overflow error in pattern

If a single pattern is too large to handle, we raise an exception. This case is
now doctested.

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