Fix "into" part of merge message for HEAD

Merging into a non-master branch would result in the following message:

  Merge branch 'a' into HEAD

Now the merge message is correct:

  Merge branch 'a' into b

Change-Id: I488f97190e4c1711c23a7a3cbd64f8b13a87bbac
Signed-off-by: Robin Stocker <robin@nibor.org>

org.eclipse.jgit.test/tst/org/eclipse/jgit/merge/MergeMessageFormatterTest.java

@@ -168,6 +168,15 @@ public class MergeMessageFormatterTest extends SampleDataRepositoryTestCase {
 		assertEquals("Merge branch 'a' into b", message);
 	}
 
+	@Test
+	public void testIntoHeadOtherThanMaster() throws IOException {
+		Ref a = db.getRef("refs/heads/a");
+		Ref b = db.getRef("refs/heads/b");
+		SymbolicRef head = new SymbolicRef("HEAD", b);
+		String message = formatter.format(Arrays.asList(a), head);
+		assertEquals("Merge branch 'a' into b", message);
+	}
+
 	@Test
 	public void testIntoSymbolicRefHeadPointingToMaster() throws IOException {
 		Ref a = db.getRef("refs/heads/a");

org.eclipse.jgit/src/org/eclipse/jgit/merge/MergeMessageFormatter.java

@@ -115,8 +115,7 @@ public class MergeMessageFormatter {
 
 		String targetName = target.getLeaf().getName();
 		if (!targetName.equals(Constants.R_HEADS + Constants.MASTER)) {
-			String targetShortName = Repository
-					.shortenRefName(target.getName());
+			String targetShortName = Repository.shortenRefName(targetName);
 			sb.append(" into " + targetShortName);
 		}