tests: index::version: add test to read index version v4

While we have a simple test to determine whether we can write an index
of version 4, we never verified that we are able to read this kind of
index (and in fact, we were not able to do so). Add a new repository
which has an index of version 4. This repository is then read from a new
test.

tests/index/version.c

@@ -9,6 +9,29 @@ void test_index_version__cleanup(void)
         g_repo = NULL;
 }
 
+void test_index_version__can_read_v4(void)
+{
+	const char *paths[] = {
+	    "file.tx", "file.txt", "file.txz", "foo", "zzz",
+	};
+	git_index *index;
+	size_t i;
+
+	g_repo = cl_git_sandbox_init("indexv4");
+
+	cl_git_pass(git_repository_index(&index, g_repo));
+	cl_assert_equal_sz(git_index_entrycount(index), 5);
+
+	for (i = 0; i < ARRAY_SIZE(paths); i++) {
+		const git_index_entry *entry =
+		    git_index_get_bypath(index, paths[i], GIT_INDEX_STAGE_NORMAL);
+
+		cl_assert(entry != NULL);
+	}
+
+	git_index_free(index);
+}
+
 void test_index_version__can_write_v4(void)
 {
 	git_index *index;

tests/resources/indexv4/.gitted/HEAD

@@ -0,0 +1 @@
+ref: refs/heads/master

tests/resources/indexv4/.gitted/config

@@ -0,0 +1,5 @@
+[core]
+	repositoryformatversion = 0
+	filemode = true
+	bare = false
+	logallrefupdates = true

tests/resources/indexv4/.gitted/refs/heads/master

@@ -0,0 +1 @@
+b0952dbb50bed5f01e03e31b296184cb183e54a7