pipe2 requires fcntl.h for its flags; PR 48614 from Steffen Daode Nurpmeso.

Also fix the wording for EINVAL as suggested by Robert Elz.

lib/libc/sys/pipe.2

@@ -1,4 +1,4 @@
-.\"	$NetBSD: pipe.2,v 1.29 2013/04/23 23:39:13 elric Exp $
+.\"	$NetBSD: pipe.2,v 1.30 2014/02/22 17:26:41 dholland Exp $
 .\"
 .\" Copyright (c) 1980, 1991, 1993
 .\"	The Regents of the University of California.  All rights reserved.
@@ -41,6 +41,8 @@
 .In unistd.h
 .Ft int
 .Fn pipe "int fildes[2]"
+.In unistd.h
+.In fcntl.h
 .Ft int
 .Fn pipe2 "int fildes[2]" "int flags"
 .Sh DESCRIPTION
@@ -134,11 +136,7 @@ will also fail if:
 .Bl -tag -width Er
 .It Bq Er EINVAL
 .Fa flags
-is other than
-.Dv O_NONBLOCK ,
-.Dv O_NOSIGPIPE
-or
-.Dv O_CLOEXEC .
+contains an invalid value.
 .El
 .Sh SEE ALSO
 .Xr sh 1 ,