.arcconfig

tests: conditionalize color output on abort

This broke in afc4ad706f9c.  I'm not sure why other aborts don't need to be
conditionalized, but `hg help foo` does abort in red for both msys and cmd.exe.

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