Add calls to bindtextdomain() and textdomain()

Currently there are two domains, one for the sudo front-end and
one for the sudoers plugin and its associated utilities.

plugins/sudoers/plugin_error.c

@@ -25,6 +25,8 @@
 #include <setjmp.h>
 #ifdef HAVE_LIBINTL_H
 # include <libintl.h>
+# undef _
+# define _(String) dgettext("sudoers", String)
 #endif
 
 #include "missing.h"