Fixed backup root path to be / instead of $HOME.

* This also means that manifest files need to use absolute paths now.
Fixed incremental backups so that are not based off the previous backup rather than the "base" directory.

* Removed the global "BACKUP_BASE" global variable.
Updated incremental backups to allow for a previous backup directory name parameter.

* Allows for the incremental backup to have a backup directory name passed to it.
* Reduces the knowledge needed by incremental backups to complete work.
Fixed backup cleanup message to not say it was completed when there was nothing to do.