xref for hthor

As some of our eclagent/hthor clusters age, we've found a number of data files on them that aren't referenced by dali. If we could get an xref "found files" function added for eclagents, it would allow for easy identification of files on disk that aren't referenced so they can either be deleted or reattached.

Granted I suspect this might be mostly due to our migration from 702 to our current builds where the user changed from root to hpcc, and someone went to delete files while they were still owned by root with the job completing since they successfully get dereferenced in dali, but likely got permission denies on the filesystem level deletion.

Regardless of that, it could allow for you to take an hthor cluster full of legitimate data and move it from dali to dali and just reattach it without the need to despray / respray.