fixed crash after a message window was closed while the search dialog was still open.
modified the order of search buttons.
removed Clear button from message search dialog.
improved the interface of message search.
reimplemented summary view with GtkTreeView.
replaced intl.h with glib/gi18n.h.
use GTK stock button for alertpanel.
use GTK stock button for button set.
Initial import of Sylpheed (GTK2 version).