subrepo: reject potentially unsafe subrepo paths (BC) (SEC) In addition to the previous patch, this prohibits '~', '$nonexistent', etc. for any subrepo types. I think this is safer, and real-world subrepos wouldn't use such (local) paths.

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