Confluence is inconsistent in error messages for restricted spaces

Synopsis:

If you browse to a specific page in a restricted space that you don't have access to, you'll receive a 404 error stating that the page cannot be found, or perhaps that you don't have access to it.

As per Matt Ryall's comment on CONF-9239, this is to ensure that we do not "leak information about the existence or non-existence of spaces which users don't have permission to see."

A few comments later in the same ticket, Charles Miller comments that you can bypass the ambiguous 404 message to get a hard "Not Permitted" or "Doesn't Exist" error when browsing to the space key directly.

If you have a restricted space with the key "RS", and the page title is "Restricted Space Home", the following is true:

1. Browsing to /display/RS/Restricted+Space+Home produces the ambigous 404 error
2. Browsing to /display/RS/ displays a "Not Permitted" action.
3. Browsing to /display/FOO/ (that doesn't exist) displays a "Page Not Found" error.