Add missing @Override tags in AlternateRepositoryDatabase

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

org.eclipse.jgit/src/org/eclipse/jgit/lib/AlternateRepositoryDatabase.java

@@ -75,14 +75,17 @@ public final class AlternateRepositoryDatabase extends ObjectDatabase {
 		return repository;
 	}
 
+	@Override
 	public void closeSelf() {
 		repository.close();
 	}
 
+	@Override
 	public void create() throws IOException {
 		repository.create();
 	}
 
+	@Override
 	public boolean exists() {
 		return odb.exists();
 	}