"Upcall handlers should be registered" -> "An upcall handler ..."

as only one handler can be registered.

lib/libc/sys/sa_enable.2

@@ -1,4 +1,4 @@
-.\"     $NetBSD: sa_enable.2,v 1.3 2004/03/14 20:57:49 wiz Exp $
+.\"     $NetBSD: sa_enable.2,v 1.4 2004/03/14 23:05:09 yamt Exp $
 .\"
 .\" Copyright (c)2004 YAMAMOTO Takashi,
 .\" All rights reserved.
@@ -44,7 +44,7 @@
 .Fn sa_enable
 is used to enable scheduler activation.
 .Pp
-Upcall handlers and upcall stacks should be registered with
+An upcall handler and upcall stacks should be registered with
 .Fn sa_register
 and
 .Fn sa_stacks

lib/libc/sys/sa_setconcurrency.2

@@ -1,4 +1,4 @@
-.\"     $NetBSD: sa_setconcurrency.2,v 1.2 2004/03/14 10:20:43 snj Exp $
+.\"     $NetBSD: sa_setconcurrency.2,v 1.3 2004/03/14 23:05:09 yamt Exp $
 .\"
 .\" Copyright (c)2004 YAMAMOTO Takashi,
 .\" All rights reserved.
@@ -54,7 +54,7 @@ However,
 won't try to allocate more virtual processors than there are physical
 processors on the system.
 .Pp
-Upcall handlers should be registered by
+An upcall handler should be registered by
 .Fn sa_register
 beforehand.
 .\" ------------------------------------------------------------

lib/libc/sys/sa_stacks.2

@@ -1,4 +1,4 @@
-.\"     $NetBSD: sa_stacks.2,v 1.3 2004/03/14 20:57:49 wiz Exp $
+.\"     $NetBSD: sa_stacks.2,v 1.4 2004/03/14 23:05:09 yamt Exp $
 .\"
 .\" Copyright (c)2004 YAMAMOTO Takashi,
 .\" All rights reserved.
@@ -51,7 +51,7 @@ is an array of
 of
 .Vt stack_t .
 .Pp
-Upcall handlers should be registered by
+An upcall handler should be registered by
 .Fn sa_register
 beforehand.
 .\" ------------------------------------------------------------