Improper 500 response for unauthorized hg command
One should get a 403 error instead of a 500 upon performing an unauthorized operation with the hg client.
Besides all the cases where a user would believe Heptapod has a problem and the various cluttering of error logs, this doesn't help understanding when it's actually Heptapod's fault. Even with !19 (merged) we'd need to understand quickly what's the matter at stake if we need to add future commands to the read-only list.