backup_phase1_client: Scan the client filesystem and send stats to the server.
backup_phase1_server: Receive the stats from the client.

backup_phase2_server: Request and receive changes from the client and create
	an unchanged list and a changed list.
backup_phase2_client: Send the changes that the server requests. The work of
	the client is now finished.

backup_phase3_server: Generate the new manifest list for the backup out of
	the unchanged list and the changed list.

backup_phase4_server: Finish off the backup by jiggling the received data
	around and putting everything in the correct place. Need to
	generate reverse deltas in order to save space for the previous backup
	(unless hardlinked_archive is turned on).
