Add a generic "object decorator" interface, and make object refs use it

This allows you to add an arbitrary "decoration" of your choice to any
object.  It's a space- and time-efficient way to add information to
arbitrary objects, especially if most objects probably do not have the
decoration.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

object.h

@@ -8,7 +8,6 @@ struct object_list {
 
 struct object_refs {
 	unsigned count;
-	struct object *base;
 	struct object *ref[FLEX_ARRAY]; /* more */
 };