#326 Implement a reverse differential mode

[Olivier Maillard]

Adding a new backup mode “reverse differential” or “reverse incremental” may be a big improvement for this very nice tools. In this mode the full backup is always a mirror of the last version of the files. The increments can be used to calculate and restore the past versions.

This mode has several advantages:
• If an increment is corrupted this only impact the restauration of old version of the files.
• Shrinking the backup can be done by simply deleting the oldest increments
• It’s very easy and fast to restore the last version of a file as you don’t need to process the increments

The plain old Rdiff-backup is able to do it see http://www.nongnu.org/rdiff-backup/
With my kinds regards
Olivier