improve wxTreeItemData documentation (closes #10662)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@60031 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/treectrl.h

@@ -774,6 +774,11 @@ public:
     /**
         Sets the item client data.
 
+        Notice that the client data previously associated with the @a item (if
+        any) is @em not freed by this function and so calling this function
+        multiple times for the same item will result in memory leaks unless you
+        delete the old item data pointer yourself.
+
         @beginWxPythonOnly
         - @b SetPyData( @a item, @c obj): Associate the given Python Object with
             the wxTreeItemData for the given item Id.