Added wxPGProperty::OnValidationFailure(); needed it and some other tweaks to allow vetoing value changes of ComboBox editors

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@58047 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/propgrid/property.h

@@ -852,6 +852,15 @@ public:
     */
     virtual wxPGEditorDialogAdapter* GetEditorDialog() const;
 
+    /**
+        Called whenever validation has failed with given pending value.
+
+        @remarks If you implement this in your custom property class, please
+                 remember to call the baser implementation as well, since they
+                 may use it to revert property into pre-change state.
+    */
+    virtual void OnValidationFailure( wxVariant& pendingValue );
+
     /**
         Append a new choice to property's list of choices.