Old backups are correctly removed, provided that
no not-to-be-removed backup depends upon them.
Incremental backups correctly start from level 0 when
there is no tar_metadata available for the last backup
Command line option --no-incremental is now incompatible
with --max-level and with --always-level
Add the following command which allows to specify
a datetime for old backup removal.
--remove-from-date YYYY-MM-DDThh:mm:ss
Closes-Bug: #1415865
Change-Id: Ie779ee354b67e9a1a012d28801b17dbd5cd353b6
LAUNCHPAD: https://bugs.launchpad.net/freezer/+bug/1415865