mod_auth_ldap, non-anon binding and openxchange support

mod_auth_ldap, non-anon binding and openxchange support

The attached patch builds on your work in the following ways:
1. adds support for non-anonymous binding.  Leaving the extra config
variables empty results in an anonymous bind.  I haven't fully tested
this (I cannot test the anonymous case), but any problems should be
apparent immediately.

2. adds support for httpd authentication.  I use mod_auth_ldap to
authenticate access to the site.  This prevents the user having to login
twice.

3. adds support for parts of the openxchange schema
(http://www.openxchange.org). Only the parts I found useful are added.
The openxchange.schema is not included as the user that enables this is
expected to have already installed openxchange.

darcs-hash:20060117111459-bb1f7-cc6f1f6e943f5c6ffa8f393f68c32500505dae67.gz