Add warning_gettext() wrapper function that changes to the user locale,

then calls gettext().
Add U_ macro that calls warning_gettext() instead of gettext().
Rename warning2()/error2() back to warning_nodebug()/error_nodebug().

src/signal.c

@@ -123,7 +123,7 @@ init_signals(void)
      * the select() loop without races (we may not have pselect()).
      */
     if (pipe_nonblock(signal_pipe) != 0)
-	fatal(_("unable to create pipe"));
+	fatal(U_("unable to create pipe"));
 
     memset(&sa, 0, sizeof(sa));
     sigfillset(&sa.sa_mask);