Make work better the (hexdump) popup menus.

Make work better the (hexdump) popup menus.

- have popup_menu_handler return TRUE or FALSE according
  to the fact that the event is really processed or not.
- use gtk_signal_connect instead of gtk_signal_connect_object
  to have the widget that emitted the signal _and_ the popup
  menu widget.
- call gtk_signal_emit_stop_by_name to abort the propagation
  if the signal was processed.

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@2318 f5534014-38df-0310-8fa8-9805f1628bb7