PURL support edge case

I've got an issue with a custom module that uses PURL and Spaces. When I create a new PURL-based Space, I want to generate a custom static 404 page (each Space has different theme elements). I can mostly use the patch from http://drupal.org/node/1331776 but when I'm creating a new Space for the first time and PURL's purl_modifiers_ cache hasn't been cleared yet (so, the Space doesn't "exist" yet), the HTTP request to fetch the 404 page's content fails. This is because the outbound_rewrite_rule hooks don't have the updated path information yet.

I've rolled a new patch (needs review) that will handle this edge case, and ensure that the prefixed path can ensure the desired path in this instance. It seems like it'll also help with similar prefixed path issues that others might encounter.