[longomatch] Fix playlists binary serialization

[Andoni Morales Alastruey <amorales src gnome org>]

commit a88c6a3ca4dde991dcbb0b407694772e0b7ef1ca
Author: Andoni Morales Alastruey <ylatuya gmail com>
Date:   Tue Aug 26 01:00:36 2014 +0200

    Fix playlists binary serialization

 .../Store/Playlists/PlaylistPlayElement.cs         |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/LongoMatch.Core/Store/Playlists/PlaylistPlayElement.cs 
b/LongoMatch.Core/Store/Playlists/PlaylistPlayElement.cs
index f194a62..0e5c2f8 100644
--- a/LongoMatch.Core/Store/Playlists/PlaylistPlayElement.cs
+++ b/LongoMatch.Core/Store/Playlists/PlaylistPlayElement.cs
@@ -15,12 +15,14 @@
 //  along with this program; if not, write to the Free Software
 //  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.
 //
+using System;
 using Newtonsoft.Json;
 using LongoMatch.Common;
 using LongoMatch.Interfaces;
 
 namespace LongoMatch.Store.Playlists
 {
+       [Serializable]
        public class PlaylistPlayElement: IPlaylistElement
        {
                public PlaylistPlayElement (Play play, MediaFile file=null)