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/control.h

@@ -56,6 +56,11 @@ public:
     virtual wxVisualAttributes GetDefaultAttributes() const;
 
 protected:
+    virtual void ApplyWidgetStyle();
+    // helper function to ease native widgets wrapping, called by 
+    // ApplyWidgetStyle -- override this, not ApplyWidgetStyle
+    virtual void DoApplyWidgetStyle(GtkRcStyle *style);
+
     virtual wxSize DoGetBestSize() const;
     void PostCreation(const wxSize& size);