pk: Add "referenced" column to hoard.chunks
pk: Add "referenced" column to hoard.chunks

- Add "referenced" column to hoard.chunks, indicating whether the chunk
has a reference in hoard.refs.  Update hoard.c accordingly.

- Bump HOARD_INDEX_VERSION

- Regularize error handling in hoard_sync_refs()

- Update cleanup_action() to print "Cleaned ..." rather than "Removed ...",
in order to make it more general

cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr