Fix issue #361 - "activate" signal on gtk.Entry uses *glib.Object as handler arg type, not *gtk.Entry
Fix issue #361 - "activate" signal on gtk.Entry uses *glib.Object as handler arg type, not *gtk.Entry

Emulate the behavior of g_cclosure_marshal_VOID__VOID in gmarshal.c in the glib library to extract the wrapped
object from GObject signal handler parameters and convert to an instance of the appropriate Go type.

gotk3/gotk3,gotk3/gotk3