Merge pull request #355 from mono/fix_tree_operations

[Xwt] Fixed/Added Tree Operations:

Xwt.Gtk/Xwt.GtkBackend/TreeStoreBackend.cs

@@ -209,7 +209,17 @@ namespace Xwt.GtkBackend
 
 		public TreePosition GetPrevious (TreePosition pos)
 		{
-			throw new NotImplementedException ();
+			IterPos tpos = GetIterPos (pos);
+			Gtk.TreePath path = Tree.GetPath (tpos.Iter);
+			int [] indices = path.Indices;
+			if (indices.Length < 1 || indices [indices.Length - 1] == 0)
+				return null;
+			indices [indices.Length - 1] --;
+			Gtk.TreePath previousPath = new Gtk.TreePath (indices);
+			Gtk.TreeIter previous;
+			if (!Tree.GetIter (out previous, previousPath))
+				return null;
+			return new IterPos (version, previous);
 		}
 
 		public TreePosition GetParent (TreePosition pos)

Xwt/Xwt/TreeNavigator.cs

@@ -94,6 +94,16 @@ namespace Xwt
 			return CommitPos (backend.GetParent (pos));
 		}
 
+		public bool MoveToFirstSibling ()
+		{
+			return CommitPos (backend.GetChild (backend.GetParent (pos), 0));
+		}
+
+		public bool MoveToLastSibling ()
+		{
+			return CommitPos (backend.GetChild (backend.GetParent (pos), backend.GetChildrenCount (backend.GetParent (pos)) - 1));
+		}
+
 		public TreeNavigator InsertBefore ()
 		{
 			pos = backend.InsertBefore (pos);

Xwt/Xwt/TreeStore.cs

@@ -92,6 +92,18 @@ namespace Xwt
 			var pos = Backend.AddChild (position);
 			return new TreeNavigator (Backend, pos);
 		}
+
+		public TreeNavigator InsertNodeAfter (TreePosition positon)
+		{
+			var pos = Backend.InsertAfter (positon);
+			return new TreeNavigator (Backend, pos);
+		}
+
+		public TreeNavigator InsertNodeBefore (TreePosition positon)
+		{
+			var pos = Backend.InsertBefore (positon);
+			return new TreeNavigator (Backend, pos);
+		}
 		
 		public void Clear ()
 		{