Add test case

tests/resources/redundant.git/HEAD

+ref: refs/heads/master

tests/resources/redundant.git/config

+[core]
+        repositoryformatversion = 0
+        filemode = true
+        bare = true
+        logallrefupdates = true

tests/resources/redundant.git/objects/info/packs

+P pack-3d944c0c5bcb6b16209af847052c6ff1a521529d.pack
+

tests/resources/redundant.git/packed-refs

+# pack-refs with: peeled fully-peeled 
+e18fa2788e9c4e12d83150808a31dfbfb1ae364f refs/heads/master
+91f4b95df4a59504a9813ba66912562931d990e3 refs/heads/ref2/ref28

tests/revwalk/mergebase.c

@@ -492,3 +492,22 @@ void test_revwalk_mergebase__octopus_merge_branch(void)
  *
  *       a
  */
+
+void test_revwalk_mergebase__remove_redundant(void)
+{
+	git_repository *repo;
+	git_oid one, two, base;
+	git_oidarray result = {NULL, 0};
+
+	cl_git_pass(git_repository_open(&repo, cl_fixture("redundant.git")));
+
+	cl_git_pass(git_oid_fromstr(&one, "d89137c93ba1ee749214ff4ce52ae9137bc833f9"));
+	cl_git_pass(git_oid_fromstr(&two, "91f4b95df4a59504a9813ba66912562931d990e3"));
+	cl_git_pass(git_oid_fromstr(&base, "6cb1f2352d974e1c5a776093017e8772416ac97a"));
+
+	cl_git_pass(git_merge_bases(&result, repo, &one, &two));
+	cl_assert_equal_i(1, result.count);
+	cl_assert_equal_oid(&base, &result.ids[0]);
+
+	git_repository_free(repo);
+}