Amend clamscan program

`clamscan` and `clamdscan` have subtle differences, it seems. The former is
meant to be run as one-off and in cron jobs; the latter is daemonized. The
former also processes the virus definitions each time it runs; the latter does
not.

`clamdscan` doesn't support the --exclude switch, whereas `clamscan` does. To
that end, the command has been changed to support `clamscan`, thereby allowing
us to exclude `lost+found` as we do not particularly care about data stored
within that folder.