Bring COPYING up to date with
http://www.gnu.org/licenses/old-licenses/gpl-2.0.txt

In the metadata.

Rather than barf later on.

If we managed to find the cover path, but we can't decompress the
data, print a warning and carry on.

So that the thumbnailer works on older versions of GNOME.

To locate the rootfile, and parsing the rootfile to know the
path of the cover image.