clone --mirror: avoid storing repeated tags

With --mirror, clone asks for refs/* already, so it does not need to
ask for ref/tags/*, too.

Noticed by Cesar Eduardo Barros.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-clone.c

diff --git a/builtin-clone.c b/builtin-clone.c
index 8612d59..c0e3086 100644
--- a/builtin-clone.c
+++ b/builtin-clone.c
@@ -330,7 +330,8 @@
 	struct ref *r;
 
 	get_fetch_map(refs, refspec, &tail, 0);
-	get_fetch_map(refs, tag_refspec, &tail, 0);
+	if (!option_mirror)
+		get_fetch_map(refs, tag_refspec, &tail, 0);
 
 	for (r = local_refs; r; r = r->next)
 		add_extra_ref(r->peer_ref->name, r->old_sha1, 0);

t/t5601-clone.sh

diff --git a/t/t5601-clone.sh b/t/t5601-clone.sh
index a13b6f9..59c65fe 100755
--- a/t/t5601-clone.sh
+++ b/t/t5601-clone.sh
@@ -95,4 +95,16 @@
 
 '
 
+test_expect_success 'clone --mirror does not repeat tags' '
+
+	(cd src &&
+	 git tag some-tag HEAD) &&
+	git clone --mirror src mirror2 &&
+	(cd mirror2 &&
+	 git show-ref 2> clone.err > clone.out) &&
+	test_must_fail grep Duplicate mirror2/clone.err &&
+	grep some-tag mirror2/clone.out
+
+'
+
 test_done