* lisp/vc/diff-mode.el (diff-vc-revisions): New defvar.
(diff-find-source-location): Call vc-find-revision for
non-nil values of 'other', diff-vc-backend, diff-vc-revisions.
* lisp/vc/vc.el (vc-diff-internal): Set buffer-local
diff-vc-revisions to the list of used revisions.
* doc/emacs/files.texi (Diff Mode): Update diff-goto-source
for VC-related prefix argument.
2ccfb4b5f4