gtk_statusbar_remove_all() was popping the top message if its
context_id matched before removing other matching messages from the
stack. This meant that if the context_id of the second top message
matched it was still displayed when the top message was popped and
then removed from the list of messages without updating the display.
Fix this by removing all the matching messages below the top one
before popping it if it matches.

https://bugzilla.gnome.org/show_bug.cgi?id=724281