made the validation message more clear

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@16082 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/treectrl/treetest.cpp

@@ -926,7 +926,7 @@ void MyTreeCtrl::OnEndLabelEdit(wxTreeEvent& event)
     // don't allow anything except letters in the labels
     if ( !event.GetLabel().IsWord() )
     {
-        wxMessageBox(wxT("The label should contain only letters."));
+        wxMessageBox(wxT("The new label should be a single word."));
 
         event.Veto();
     }