hgweb: Respond with HTTP 403 for disabled archive types instead of 404
This makes it easier for clients/users to distinct between supported
but disabled and unsupported archive types.
Ancestors of 5
4 2 0
Ancestors of 6 and 5
3 4 2 1 0
Ancestors of 5 and 4
4 2 0
Descendants of 5
7 8
Descendants of 5 and 3
6 7 8
Descendants of 5 and 4
5 7 8