add common fsck error printing function

Signed-off-by: Martin Koegler <mkoegler@auto.tuwien.ac.at>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

fsck.h

@@ -17,6 +17,8 @@ typedef int (*fsck_walk_func)(struct object *obj, int type, void *data);
 /* callback for fsck_object, type is FSCK_ERROR or FSCK_WARN */
 typedef int (*fsck_error)(struct object *obj, int type, const char *err, ...);
 
+int fsck_error_function(struct object *obj, int type, const char *fmt, ...);
+
 /* descend in all linked child objects
  * the return value is:
  *    -1	error in processing the object