fixed GTK styles handling:

1. don't modify the style unless something changed
2. use gtk_widget_modify_style instead of gtk_widget_set_style, the latter is not recommended by GTK+ developers


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@27784 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/gtk/checkbox.h

@@ -51,7 +51,7 @@ public:
     // implementation
     // --------------
 
-    void ApplyWidgetStyle();
+    void DoApplyWidgetStyle(GtkRcStyle *style);
     bool IsOwnGtkWindow( GdkWindow *window );
     void OnInternalIdle();