Add EXIT STATUS section. From Ryan Kavanagh via jmc@openbsd.

Bump date. Remove unnecessary quotes.

XXX: The behaviour is now documented as-is, but it is weird.
"biff n; biff y" has an exit status of 1 because biff reports the
notification status when it was started, not after it has finished.
{Free,Open}BSD's biff behave the same, but it's unclear if it's intended
or a bug.

usr.bin/biff/biff.1

@@ -1,4 +1,4 @@
-.\"	$NetBSD: biff.1,v 1.9 2003/08/07 11:13:12 agc Exp $
+.\"	$NetBSD: biff.1,v 1.10 2013/04/28 12:43:51 wiz Exp $
 .\"
 .\" Copyright (c) 1980, 1990, 1993
 .\"	The Regents of the University of California.  All rights reserved.
@@ -29,12 +29,12 @@
 .\"
 .\"     @(#)biff.1	8.1 (Berkeley) 6/6/93
 .\"
-.Dd June 6, 1993
+.Dd April 28, 2013
 .Dt BIFF 1
 .Os
 .Sh NAME
 .Nm biff
-.Nd "be notified if mail arrives and who it is from"
+.Nd be notified if mail arrives and who it is from
 .Sh SYNOPSIS
 .Nm
 .Op Cm ny
@@ -72,6 +72,18 @@ or the
 .Ar mail
 variable of
 .Xr csh 1 .
+.Sh EXIT STATUS
+The
+.Nm
+utility exits with one of the following values:
+.Bl -tag -width indent
+.It 0
+Notification was enabled at the time of invocation.
+.It 1
+Notification was disabled at the time of invocation.
+.It >1
+An error occurred.
+.El
 .Sh SEE ALSO
 .Xr csh 1 ,
 .Xr mail 1 ,