bug#24661: [RFE] Allow running shred on directories

[Mohammed Sadiq]

This is a request for enhancement.

It might be nice to allow users to run shred on directories which
would recursively shred the directory and its contents. This may be
limited to happen only when `-u' flag is used.

Possible use case:
1. The user have to delete several files, along with nested directories.
    shred command on directory may shred each containing files and
shred them, then rename the directory to 000... (The same way as files
are handled).

I find overwriting with Zeros a nice idea, but I have no lazy way to
do that for directories with any available tools.

Thanks