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/defs.h

@@ -2342,7 +2342,7 @@ typedef struct _GdkICAttr       GdkICAttr;
 
 /* Stand-ins for GTK types */
 typedef struct _GtkWidget         GtkWidget;
-typedef struct _GtkStyle          GtkStyle;
+typedef struct _GtkRcStyle        GtkRcStyle;
 typedef struct _GtkAdjustment     GtkAdjustment;
 typedef struct _GtkList           GtkList;
 typedef struct _GtkToolbar        GtkToolbar;