Tentative built-in "git show"

This uses the "--no-walk" flag that I never actually implemented (but I'm
sure I mentioned it) to make "git show" be essentially the same thing as
"git whatchanged --no-walk".

It just refuses to add more interesting parents to the revision walking
history, so you don't actually get any history, you just get the commit
you asked for.

I was going to add "--no-walk" as a real argument flag to git-rev-list
too, but I'm not sure anybody actually needs it. Although it might be
useful for porcelain, so I left the door open.

[jc: ported to the unified option structure by Linus]

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>
diff --git a/revision.c b/revision.c
index 9693b6e..f8fb028 100644
--- a/revision.c
+++ b/revision.c
@@ -380,6 +380,9 @@
 	if (revs->prune_fn)
 		revs->prune_fn(revs, commit);
 
+	if (revs->no_walk)
+		return;
+
 	parent = commit->parents;
 	while (parent) {
 		struct commit *p = parent->item;
@@ -816,6 +819,8 @@
 		list = list->next;
 	}
 
+	if (revs->no_walk)
+		return;
 	if (revs->limited)
 		limit_list(revs);
 	if (revs->topo_order)