vc mode enhancement proposal

[Neal Becker]

If I edit a version-controlled, hard-linked file, no backup is made (cause
it's version-controlled), and the results is the editing does not break
the hard link.

Sometimes that's what I want.  Other times it's not.

I don't know how to get emacs to break the hard link.

What I think we need is to add vc-make-backups-when-linked.