Replace GDK_<keyname> macros with GDK_KEY_<keyname>.
(Since GTK+ 2.21.8, backward-compatibility code not added yet.)
Add backward-compatible GDK_<keyname> macros in mygtk.h
Replace GTK_OBJECT() type cast with G_OBJECT() in g_signal_connect() arguments
Remove useless gtk_set_locale() call. Manual says gtk_init() does this and I get compile error when I don't remove it.