configure: add AM_GNU_GETTEXT_VERSION([0.17]) and AM_GNU_GETTEXT([external])
configure: add AM_GNU_GETTEXT_VERSION([0.17]) and AM_GNU_GETTEXT([external])

Without it ENABLE_NLS is not set in config.h so we don't get gsv translated.

GNOME/gtksourceview,cburschka/gtksourceview,cburschka/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,uajain/gtksourceview,uajain/gtksourceview,cburschka/gtksourceview,cburschka/gtksourceview,uajain/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,cburschka/gtksourceview,cburschka/gtksourceview,GNOME/gtksourceview,cburschka/gtksourceview,cburschka/gtksourceview,uajain/gtksourceview,cburschka/gtksourceview,uajain/gtksourceview,cburschka/gtksourceview,GNOME/gtksourceview,uajain/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,uajain/gtksourceview,uajain/gtksourceview,GNOME/gtksourceview,uajain/gtksourceview,GNOME/gtksourceview,uajain/gtksourceview