Really handle annotated tags in MergeCommand

Repository.peel() must be called to ensure a tag is really peeled.

Change-Id: I83e25f09fad3ad55a3ffe41ab4758f249b7ac9f9

org.eclipse.jgit/src/org/eclipse/jgit/api/MergeCommand.java

@@ -234,6 +234,7 @@ public class MergeCommand extends GitCommand<MergeResult> {
 			refLogMessage.append(ref.getName());
 
 			// handle annotated tags
+			ref = repo.peel(ref);
 			ObjectId objectId = ref.getPeeledObjectId();
 			if (objectId == null)
 				objectId = ref.getObjectId();