Restrict Certain Subfolders

This simple patch adds a new field that allows you to enter a comma-delimited list of sub-folders in a user's main folder that they can access (assuming that Enable Subfolder Navigation is checked) - all others will not be shown. If the list is empty, all sub-folders are shown (as they normally are by default).

I created this because there isn't a way to currently (in version 5 - I think there is now in v6) allow access to multiple shared folders. I have a root folder that I want to give someone access to, but not ALL the folders in it, just some. This patch allow you to do just that.

I've tested this, however, I would like others to do the same before using this in a production environment.