kqueue support for OpenLDAP (ITS#6300)

[Quanah Gibson-Mount <quanah@symas.com>]

A long long time ago for a release that is now far far away, Apple 
submitted a patch adding kqueue support to OpenLDAP.  I managed to track it 
down and have it working with some changes since the patch was originally 
written for OpenLDAP 2.3.  In OpenLDAP master, it passed all tests with 
back-meta, back-ldap, back-meta backends along with the accesslog, 
syncprov, and rwm overlays.  I think it generally is good to go in as a 2.5 
feature.  If anyone else would like to test it, they would need to run 
autoconf first to pick up the configure changes.

Branch is:
<https://github.com/quanah/openldap-scratch/tree/its6300>

Commits are:

<https://github.com/quanah/openldap-scratch/commit/d0c29a30c4cd7c0ab192d930109c348984354813>
<https://github.com/quanah/openldap-scratch/commit/7ebbf79a07e684696f75c912e92d435d8552d24e>

The only real changes are to servers/slapd/daemon.c, the rest are basically 
the header check & function check for configure.

The one bit I wasn't sure on is if the handling of 
SLAP_EVENT_IS_(READ|WRITE) in slapd_daemon_task is the best way to address 
that KQUEUE requires the thread id while event/poll do not (Starting around 
line 2942).  If there's a better way to do this other than the ifdefs, let 
me know, and I'll update accordingly.

Thanks!

--Quanah

--

Quanah Gibson-Mount
Product Architect
Symas Corporation
Packaged, certified, and supported LDAP solutions powered by OpenLDAP:
<http://www.symas.com>