git-show: Reject native ref

So when we do

	git show v1.4.4..v1.5.0

that's an illogical thing to do, since "git show" is defined to be a
non-revision-walking action, which means the range operator be pointless
and wrong. The fact that we happily accept it (and then _only_ show
v1.5.0, which is the positive end of the range) is quite arguably not very
logical.

We should complain, and say that you can only do "no_walk" with positive
refs. Negative object refs really don't make any sense unless you walk
the obejct list (or you're "git diff" and know about ranges explicitly).

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

revision.c

@@ -116,6 +116,8 @@ void mark_parents_uninteresting(struct commit *commit)
 
 void add_pending_object(struct rev_info *revs, struct object *obj, const char *name)
 {
+	if (revs->no_walk && (obj->flags & UNINTERESTING))
+		die("object ranges do not make sense when not walking revisions");
 	add_object_array(obj, name, &revs->pending);
 	if (revs->reflog_info && obj->type == OBJ_COMMIT)
 		add_reflog_for_walk(revs->reflog_info,