ITS #6300: Added support for using kqueue in slapd (for systems that support kqueue(2).

ITS #6300: Added support for using kqueue in slapd (for systems that support kqueue(2).

Patch obtained from:
        http://public.me.com/bryan.duncan/bryan-duncan.kqueue.090922.patch

 # This patch file is derived from OpenLDAP Software. All of the
 # modifications to OpenLDAP Software represented in the following
 # patch(es) were developed by Apple.  I, Bryan Duncan, am authorized by
 # Apple, my employer, to release this work under the following terms.
 #
 # Copyright 2009 Apple Inc. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted only as authorized by the OpenLDAP
 # Public License.
 #
 # A copy of this license is available in file LICENSE in the
 # top-level directory of the distribution or, alternatively, at
 # http://www.OpenLDAP.org/license.html.
 #