gio: Add source tags to various GTasks constructed in GLib

This makes them easier to identify when debugging and profiling.

This patch was somewhat less than interesting to write.

https://bugzilla.gnome.org/show_bug.cgi?id=767765

gio/gdbusaddress.c

@@ -865,6 +865,7 @@ g_dbus_address_get_stream (const gchar         *address,
   data->address = g_strdup (address);
 
   task = g_task_new (NULL, cancellable, callback, user_data);
+  g_task_set_source_tag (task, g_dbus_address_get_stream);
   g_task_set_task_data (task, data, (GDestroyNotify) get_stream_data_free);
   g_task_run_in_thread (task, get_stream_thread_func);
   g_object_unref (task);