gtkdialog: separator widget reference

# separator widget A GtkSeparatorMenuItem ## Notes This widget has been deprecated since 0.7.21 and menuitemseparator should be used instead. button, checkbox, chooser, colorbutton, comboboxentry, comboboxtext, combobox, edit, entry, eventbox, expander, fontbutton, frame, hbox, hscale, hseparator, list, menubar, menuitemseparator, menuitem, menu, notebook, pixmap, progressbar, radiobutton, separator, spinbutton, statusbar, table, terminal, text, timer, togglebutton, tree, vbox, vscale, vseparator, window,