RefDirectory: Do not use search path to find additional refs

Psuedorefs like FETCH_HEAD and MERGE_HEAD are supposed to be directly
under the .git directory, not in other locations in the SEARCH_PATH
like refs/ and refs/heads/.  Use exactRef to access them.

Change-Id: Iab8ac47008822fa78fc0691e239e518c34d7a98e
Signed-off-by: Jonathan Nieder <jrn@google.com>

org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/file/RefDirectoryTest.java

@@ -48,6 +48,7 @@ import static org.eclipse.jgit.lib.Constants.R_HEADS;
 import static org.eclipse.jgit.lib.Constants.R_TAGS;
 import static org.eclipse.jgit.lib.Ref.Storage.LOOSE;
 import static org.eclipse.jgit.lib.Ref.Storage.NEW;
+import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
@@ -1098,6 +1099,28 @@ public class RefDirectoryTest extends LocalDiskRepositoryTestCase {
 		assertNull(refdir.exactRef("v1.0"));
 	}
 
+	@Test
+	public void testGetAdditionalRefs_OrigHead() throws IOException {
+		writeLooseRef("ORIG_HEAD", A);
+
+		List<Ref> refs = refdir.getAdditionalRefs();
+		assertEquals(1, refs.size());
+
+		Ref r = refs.get(0);
+		assertFalse(r.isSymbolic());
+		assertEquals(A, r.getObjectId());
+		assertEquals("ORIG_HEAD", r.getName());
+		assertFalse(r.isPeeled());
+		assertNull(r.getPeeledObjectId());
+	}
+
+	@Test
+	public void testGetAdditionalRefs_OrigHeadBranch() throws IOException {
+		writeLooseRef("refs/heads/ORIG_HEAD", A);
+		List<Ref> refs = refdir.getAdditionalRefs();
+		assertArrayEquals(new Ref[0], refs.toArray());
+	}
+
 	@Test
 	public void testGetRef_FetchHead() throws IOException {
 		// This is an odd special case where we need to make sure we read

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/RefDirectory.java

@@ -412,7 +412,7 @@ public class RefDirectory extends RefDatabase {
 	public List<Ref> getAdditionalRefs() throws IOException {
 		List<Ref> ret = new LinkedList<>();
 		for (String name : additionalRefsNames) {
-			Ref r = getRef(name);
+			Ref r = exactRef(name);
 			if (r != null)
 				ret.add(r);
 		}