Added support for symlinked directories.

In relation to this issue: https://github.com/laurilehmijoki/s3_website/issues/3 

I've pushed a fix in filey-diff (https://github.com/laurilehmijoki/filey-diff/pull/5) and also added this small change to fix the issue. Symlinks should now be followed to one depth (to prevent recursive links). 

I might have missed out other directory traversals. I am also not familiar with ruby so you might want to review it.