Document that the *printf() functions can return a negative value under

output error conditions.

lib/libc/stdio/printf.3

@@ -1,4 +1,4 @@
-.\"	$NetBSD: printf.3,v 1.27 2002/10/01 17:24:06 wiz Exp $
+.\"	$NetBSD: printf.3,v 1.28 2002/11/11 17:26:19 simonb Exp $
 .\"
 .\" Copyright (c) 1990, 1991, 1993
 .\"	The Regents of the University of California.  All rights reserved.
@@ -119,6 +119,8 @@ the number of characters printed
 (not including the trailing
 .Ql \e0
 used to end output to strings).
+If an output error was encountered, these functions shall return a
+negative value.
 .Pp
 .Fn asprintf
 and