Backups only for changed database file

[marvinweber]

New option to only make backups, if the database actually has changed since last backup.

This requires to store the hash of the last backup (of the db file) somewhere (this should work per backup location)

[ElTopo]

I personally recommend that don't waste time on this. It's pretty hard for a plugin to figure out if a database has been changed or not. If user press "Save" button, from the POV of the plugin, it should just assume the database is changed somehow.
On the other hand, backups are backups, they are saved data with timestamp, it doesn't matter if two backups are identical or not.