Multiple Path Prefix and Path Alias

Issue Summary

f you use PURL with multiple path prefix and you have a node-alias that contains the prefix. PURL handle all parts of the url as prefix.

For Example. 1 Prefix per Section and User/Person
1. prefix: management
2. prefix: john

System-URL => Alias
node/10 => john/vita

john/vita => node/10
=> OK

management/john/node/10
=> OK (2 prefix + drupal system path)

management/john/vita
=> Redirect to front. (PURL handle arg(0) and arg(1) as prefix) -> /vita is no valid url
=> But this is a Valid URL: 1 prefix + path-alias

management/john/john/vita
=> OK, 2 prefix + path-alias

To solve this problem, PURL have to respect the node-alias and stop rewrite these urls. Here is a patch to do this. Please test and review. Has anyone a better approach to do this?