branch.c: use the parsed branch name

When setting up tracking info, branch.c uses the given branch specifier
("name"). Use the parsed name ("ref.buf") instead so that

git branch --set-upstream @{-1} foo

sets up tracking info for the previous branch rather than for a branch
named "@{-1}".

Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

branch.c

@@ -210,7 +210,7 @@ void create_branch(const char *head,
 			 start_name);
 
 	if (real_ref && track)
-		setup_tracking(name, real_ref, track);
+		setup_tracking(ref.buf+11, real_ref, track);
 
 	if (!dont_change_ref)
 		if (write_ref_sha1(lock, sha1, msg) < 0)

t/t6040-tracking-info.sh

@@ -110,4 +110,18 @@ test_expect_success '--set-upstream does not change branch' '
 	grep -q "^refs/heads/master$" actual &&
 	cmp expect2 actual2
 '
+
+test_expect_success '--set-upstream @{-1}' '
+	git checkout from-master &&
+	git checkout from-master2 &&
+	git config branch.from-master2.merge > expect2 &&
+	git branch --set-upstream @{-1} follower &&
+	git config branch.from-master.merge > actual &&
+	git config branch.from-master2.merge > actual2 &&
+	git branch --set-upstream from-master follower &&
+	git config branch.from-master.merge > expect &&
+	test_cmp expect2 actual2 &&
+	test_cmp expect actual
+'
+
 test_done