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/spinbutt.h

@@ -53,7 +53,6 @@ public:
     void OnSize( wxSizeEvent &event );
 
     bool IsOwnGtkWindow( GdkWindow *window );
-    void ApplyWidgetStyle();
 
     GtkAdjustment  *m_adjust;
     float           m_oldPos;