Fixup menu for GTK3

xdot.py

@@ -2013,7 +2013,7 @@ def __init__(self, command_line_files, widget=None):
 
         # Connect the Button click event of the drawing menu, in order
         # to display a file menu
-        self.widget.connect("button-press-event", self.on_file_menu)
+        self.dotwidget.connect("button-press-event", self.on_file_menu)
 
         self.connect('key-press-event', self.on_key_press_event)
 
@@ -2158,21 +2158,25 @@ def on_go_back(self, action = None):
         self.open_file(self.open_files[self.open_file_idx])
 
     def on_file_menu(self, widget, event):
-        if event.type == gtk.gdk.BUTTON_PRESS and event.button == 3:
-            menu = gtk.Menu()
+        if event.type == Gdk.EventType.BUTTON_PRESS and event.button == 3:
+            menu = Gtk.Menu()
             for filename in self.open_files:
                 label = os.path.basename(filename)
-                item  = gtk.MenuItem(label)
-                menu.append(item)
+                item  = Gtk.MenuItem()
+                item.set_label(label)
                 item.connect("activate", lambda _, f: self.open_file(f), filename)
-                item.show()
-            menu.popup(None, None, None, 3, event.time)
+                menu.append(item)
+                menu.show_all()
+            self.menu = menu
+            menu.popup(None, None, None, None,
+                       event.button, event.time)
+            return True
 
     def on_key_press_event(self, widget, event):
-        if event.keyval == gtk.keysyms.bracketleft:
+        if event.keyval == Gdk.KEY_bracketleft:
             self.on_go_back()
             return True
-        if event.keyval == gtk.keysyms.bracketright:
+        if event.keyval == Gdk.KEY_bracketright:
             self.on_go_forward()
             return True