Mac: Detect newly created symbolic links

[wilbaker]

#285 added support for projecting symbolic links, but VFS for Git still needs to detect when they are created and update the Modified Paths database so that the new links are reported by git status

[wilbaker]

One option here:

• Notify VFS4G when a child is being added to a folder
• VFS4G can check for new children in that folder in the pre-command hook
• TBD: When to purge the list of folders to check, perhaps after view changes?