include gtk/gtk.h as a workaround for GTK+ >= 2.13.3.
added 'To' column to the summary view.
win32: made a workaround for the redraw problem in GTK+ 2.10.11.
improved the display items dialog.
set toolbar customization dialog title and label.
implemented the toolbar customization of the composition window.
fixed focus problem in win32.
separated UI code from prefs.c.
made the order of buttons comply with GNOME HIG.
reimplemented summary view with GtkTreeView.
replaced intl.h with glib/gi18n.h.
use GTK stock button for button set.
Initial import of Sylpheed (GTK2 version).