www: cgit: fall back to WwwCoderepo on 404s

www: cgit: fall back to WwwCoderepo on 404s

We can't rely on 3-element array response when calling
WwwCoderepo for ViewVCS endpoints since that uses Qspawn
internally.  Thus, we have to allow two Qspawn objects to run in
parallel and ensure `qspawn.wcb' only gets called once, so we
end up duplicating the entire $ctx to ensure this.