libc: add ftw / nftw functions

Please see "man 3 ftw" for a description of the
ftw / nftw functions.

This code is taken directly from netbsd unmodified.

Change-Id: Ia4879ac57212b424adf5281b5e92858e216d0f14
diff --git a/libc/NOTICE b/libc/NOTICE
index 4cc28dc..299f672 100644
--- a/libc/NOTICE
+++ b/libc/NOTICE
@@ -3421,6 +3421,26 @@
 
 -------------------------------------------------------------------
 
+Copyright (c) 2003 Todd C. Miller <Todd.Miller@courtesan.com>
+
+Permission to use, copy, modify, and distribute this software for any
+purpose with or without fee is hereby granted, provided that the above
+copyright notice and this permission notice appear in all copies.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+
+Sponsored in part by the Defense Advanced Research Projects
+Agency (DARPA) and Air Force Research Laboratory, Air Force
+Materiel Command, USAF, under agreement number F39502-99-1-0512.
+
+-------------------------------------------------------------------
+
 Copyright (c) 2004 The NetBSD Foundation, Inc.
 All rights reserved.