Using "Next unread message" not quite as expected

In a recent mailing list thread, Andreas reported a problem with Balsa's message window: selecting the next unread message changes the message in the preview pane, but not in the message window. Other changes to the displayed message may have a similar issue.

The cause seems to be a change in the way GtkTreeSelection's "changed" signal is emitted. When a different message is selected using gtk_tree_view_set_cursor(), the signal used to be emitted synchronously, so the caller could assume that the signal handler had been called before gtk_tree_view_set_cursor() returned. That seems to be no longer the case.