If you need to run directory listings through various filters and transforms,
File_Util::listDir is your friend, especially with the recently added callback
final arg.

Check out recent Seagull code updates to see the flexibility of the current approach,
we need to consolidate all Seagull directory methods in order for next step of
front controller to be implemented.

getAllNavDrivers() is the first converted method, it makes use of callbacks,
lambda fns and pass-by-ref to update filtered dir listings.