gtkglarea: gtk_widget_[push|pop]_visual is a noop nowadays
gtkgl/gtkglarea.c: Use accesor functions to access widget flags
examples: Use more accessor funtions
examples/zktor.c: Fix a GTK_OBJECT -> G_OBJECT leftover
examples/zktor.c: gtk_idle_add - > g_idle_add
examples/viewlw.c: Use gtk_menu_shell_append() instead deprecated gtk_menu_append()
examples/viewlw.c: Replace deprecated gtk_widget_draw()