GNOME 3: Add "Close" button to about box

Otherwise the user would have to close the modal
about dialog with Escape, which might not be very
usable for users which are not used to this key.

src/gpodder/gtkui/main.py

@@ -3076,6 +3076,7 @@ class gPodder(BuilderWidget, dbus.service.Object):
     def on_itemAbout_activate(self, widget, *args):
         dlg = gtk.Dialog(_('About gPodder'), self.main_window, \
                 gtk.DIALOG_MODAL)
+        dlg.add_button(gtk.STOCK_CLOSE, gtk.RESPONSE_OK).show()
         dlg.set_resizable(False)
 
         bg = gtk.HBox(spacing=10)
@@ -3149,7 +3150,6 @@ class gPodder(BuilderWidget, dbus.service.Object):
             sw.hide()
 
         credits.grab_focus()
-        dlg.action_area.hide()
         dlg.run()
 
     def on_wNotebook_switch_page(self, notebook, page, page_num):