Add --with-empty-directories option to list-files command

[gbroccolo]

When executing the list-files command, empty directories are not included. However, having them in this list, would simplify integration with tar and subsequent recovery operations.

We suggest to add an option called "--with-empty-directories" or similar, by default set to false.

[richyen]

In terms of implementing this, we could:

• List all dirs and their contents
• List all contents and then dirnames of empty dirs only
• List all contents and all dirnames
• List all contents and dirnames of empty dirs, making the empty dirs with a trailing backslash
• Something else?

What would be the proposed implementation of this enhancement?