Modify backup scripts to save off copies outside Cassandra's tree
Also delete old backup files from the external backup directory
Create backup directory if it doens't exist
Missing $
Use [] for optional parameters
Sanity check that we have backups in list_backups
Guard against rm -rf in incorrect directory
Invert directory structure with backups so they are grouped by snapshot, rather than table
Give up on timestamp
Merge pull request #28 from Metaswitch/enhance-backup

Reviewer Matt: Enhance backup