Patch delete_file_node function, create bonus (copy)

Patch delete_file_node function, create bonus (copy)

The function delete_file_node made the static list NULL when deleting
the first entry. When there is more than a single entry in the list this
leads to loss the rest of the list. When get_next_line would be called
on file descriptor saved in such a "forgotten" list, it would not be
able to retrieve the data previously loaded to the files buffer.

Because bonus functions were implemented in the basic files, bonus files
are created by their duplication. This is needed to let moulinette
recognize bonus.