Annotate all custom GIO GSource using g_source_set_name

Naming the sources allows easier debugging with e.g. SystemTap
probes.

https://bugzilla.gnome.org/show_bug.cgi?id=620536

gio/gsocket.c

@@ -2401,6 +2401,7 @@ socket_source_new (GSocket      *socket,
   condition |= G_IO_HUP | G_IO_ERR;
 
   source = g_source_new (&socket_source_funcs, sizeof (GSocketSource));
+  g_source_set_name (source, "GSocket");
   socket_source = (GSocketSource *)source;
 
   socket_source->socket = g_object_ref (socket);