Fix empty .No macros, use .Pf to prefix delimiters to macros.

Based on a patch from guenther@, tweaked by me.
OK jmc@ guenther@

diff --git a/lib/libc/gen/ftw.3 b/lib/libc/gen/ftw.3
index 7aa5347..4967bb7 100644 (file)
--- a/lib/libc/gen/ftw.3
+++ b/lib/libc/gen/ftw.3
@@ -1,4 +1,4 @@
-.\"    $OpenBSD: ftw.3,v 1.11 2014/01/21 03:15:45 schwarze Exp $
+.\"    $OpenBSD: ftw.3,v 1.12 2015/10/11 21:23:24 schwarze Exp $
 .\"
 .\" Copyright (c) 2003 Todd C. Miller <Todd.Miller@courtesan.com>
 .\"
@@ -18,7 +18,7 @@
 .\" Agency (DARPA) and Air Force Research Laboratory, Air Force
 .\" Materiel Command, USAF, under agreement number F39502-99-1-0512.
 .\"
-.Dd $Mdocdate: January 21 2014 $
+.Dd $Mdocdate: October 11 2015 $
 .Dt FTW 3
 .Os
 .Sh NAME
@@ -89,7 +89,7 @@ A directory which cannot be read.
 The directory will not be descended into.
 .It Dv FTW_DP
 A directory being visited in post-order
-.No ( Ns Fn nftw
+.Pf ( Fn nftw
 only).
 .It Dv FTW_NS
 A file for which no
@@ -100,7 +100,7 @@ The contents of the stat structure are undefined.
 A symbolic link.
 .It Dv FTW_SLN
 A symbolic link with a non-existent target
-.No ( Ns Fn nftw
+.Pf ( Fn nftw
 only).
 .El
 .Pp