Removing backup files corresponding to no longer existing files

[Rasmus Villemoes <burner+usenet@imf.au.dk>]

Hi,

I use a couple of separate directories to store emacs backup files
(using backup-directory-alist). But this means that if I decide to
delete or move some project (which is in its own direcory), just
deleting or moving the directory leaves all the backup copies
behind. They will then stay in the backup directories forever.

Is there a way to tell emacs to remove backup files which no longer
correspond to an actual file?

It's probably not very difficult to write a little (shell/perl) script
to do this, but I was wondering if there is some builtin way which
I've overlooked.

Emacs 23.1.1 on Ubuntu 10.10, if it matters.

Thanks in advance,
Rasmus