Expose full torrent directory structure in content_files

Currently the directory structure inside the torrent (if any) is removed prior to adding to entry['content_files']. This makes the structure opaque to any other plugin that may need it (such as a downloading plugin). This change passes the full directory structure along with the filename.

As discussed in IRC the only affected plugin is content_filter and this actually should make the behavior consistent with torrent.py (which reads a torrent file and, amongst other things provides the full directory structure in content_files).