cmdutil: allow native string as input to check_at_most_one_arg() We seem to always convert **opts args to use bytes as keys early on in Mercurial core, but I'm not sure we have good reason to do that, and not all extensions do that. It's therefore helpful to be able to pass in a native string to check_at_most_one_arg(). Differential Revision: https://phab.mercurial-scm.org/D7699