User defined signals for GtkWidget

[Matthias Mann <matman matman24 org>]

In an older documentation of Gtk+ i saw this function:
   
gtk_object_class_user_signal_new()
   
This could be a good solution for adding a special needed
signal to an existing GtkWidget without creating a new
object based on the needed widget class. But this feature
seems to be removed from Gtk2.x. Had nothing found about in
API. Is there a similar possibility to add a user defined
signal to a widget?
   
Mathew