Making a backup file on every buffer save?

[Roy Smith]

The docs say:

"Emacs makes a backup for a file only the first time the file is
saved from a buffer.  No matter how many times you subsequently save
the file, its backup remains unchanged.  However, if you kill the
buffer and then visit the file again, a new backup file will be made."

Is there any way to override this and get a backup file on every
buffer save?  I'm using GNU Emacs 23.1.1.

I recently managed to blow away a file on disk that I had been editing
and no longer had a copy in an emacs buffer.  I had the backup from
the last time I had visited the file, but had done a lot of work since
then and had saved many intermediate versions.  If those intermediate
saves had generated backups, I would have avoided losing a bunch of
work.  The disk and CPU costs for this are trivial on modern hardware.