Add support for performing remote object copies using the 'copy-from'
operation.

[ Add COPY_FROM to get_num_data_items(). ]
Signed-off-by: NLuis Henriques <lhenriques@suse.com>
Reviewed-by: NIlya Dryomov <idryomov@gmail.com>
Signed-off-by: NIlya Dryomov <idryomov@gmail.com>