(occur-engine): Initial *Occur* output not undoable.

lisp/replace.el

@@ -1061,6 +1061,8 @@ See also `multi-occur'."
 			    title-face prefix-face match-face keep-props)
   (with-current-buffer out-buf
     (let ((globalcount 0)
+	  ;; Don't generate undo entries for creation of the initial contents.
+	  (buffer-undo-list t)
 	  (coding nil))
       ;; Map over all the buffers
       (dolist (buf buffers)