Always download same torrrent to same subdirectory

[noctuid]

It might be nice if btfs would reuse the same directory for the same torrent instead of generating new directories with each mount (e.g. if the directory was <btfs data directory>/<torrent info hash>). It would be great if a mount could then reuse old data if --keep was specified. Not sure if that is possible.

[johang]

This idea makes sense. I don't remember why I chose the current mkdtemp approach. Should be possible to setup p.save_path in populate_metadata based on information in p.ti.