implement popup/context menu

implement popup/context menu

	* ../src/pgtkterm.c (x_draw_glyph_string_background)
	(x_draw_glyph_string_foreground)
	(x_draw_composite_glyph_string_foreground)
	(x_draw_glyphless_glyph_string_foreground, x_draw_relief_rect)
	(x_draw_box_rect, x_draw_glyph_string_box, x_draw_image_relief)
	(x_draw_image_foreground, x_draw_image_glyph_string)
	(button_event):

	* src/pgtkterm.h (struct pgtk_display_info):

	* src/pgtkmenu.c (pgtk_menu_set_in_use)
	(pgtk_menu_wait_for_event, Fx_menu_bar_open_internal)
	(popup_widget_loop, pgtk_activate_menubar)
	(popup_deactivate_callback, show_help_event): new functions
	(menu_highlight_callback): remove
	(update_frame_menubar, popup_selection_callback, pop_down_menu)
	(create_and_show_popup_menu, cleanup_widget_value_tree)
	(pgtk_menu_show, dialog_selection_callback): new
	(create_and_show_dialog, pgtk_dialog_show, pgtk_popup_dialog)
	(popup_activated, Fmenu_or_popup_active_p, syms_of_pgtkmenu):