StatusIcon: dispose properly

Override Dispose method of Component class, so it calls the backend's
Dispose method.

Xwt.Mac/Xwt.Mac/StatusIconBackend.cs

@@ -62,6 +62,12 @@ namespace Xwt.Mac
 		
 		public void EnableEvent (object eventId) { throw new NotImplementedException (); }
 		public void DisableEvent (object eventId) { throw new NotImplementedException (); }
+
+		public void Dispose ()
+		{
+			statusItem.Dispose ();
+			statusItem = null;
+		}
 	}
 }
 

Xwt/Xwt.Backends/IStatusIconBackend.cs

@@ -29,7 +29,7 @@ using System.Collections.ObjectModel;
 
 namespace Xwt.Backends
 {
-	public interface IStatusIconBackend : IBackend
+	public interface IStatusIconBackend : IBackend, IDisposable
 	{
 		void SetMenu (object menuBackend);
 		

Xwt/Xwt/StatusIcon.cs

@@ -54,6 +54,16 @@ namespace Xwt
 		IStatusIconBackend Backend {
 			get { return (IStatusIconBackend) BackendHost.Backend; }
 		}
+		
+		protected override void Dispose (bool disposing)
+		{
+			base.Dispose (disposing);
+			
+			// Don't dispose the backend if this object is being finalized
+			// The backend has to handle the finalizing on its own
+			if (disposing && BackendHost.BackendCreated)
+				Backend.Dispose ();
+		}
 	}
 }