CacheManager scans the cache directory during initialization.

CacheManager scans the cache directory during initialization.

Actually the scanning is done after a successful join so that
files can be added to the DHT.

The HashObjects can now hash a file in a separate thread.

The donwload cache is scanned for new files too, causing the
decompressed versions of compressed Packages files to be
hashed and added to the DHT. This isn't currently consistent
since they are not added when they are first downloaded
and decompressed.