LDAP deprecations in PHP 7.4

ldap_control_paged_result_response and ldap_control_paged_result are
deprecated. Pagination controls can be sent along with ldap_search instead.

That means, unless I'm wrong, that we'll have to use LDAP controls within ldap_search() instead.

Problem is that LDAP controls are only available for php73 and up, so we'll need to perform some interim conditional code: one solution for php71-72 and another for php73-74.

Links:

LDAP search: https://www.php.net/manual/en/function.ldap-search.php
LDAP controls: https://www.php.net/manual/en/ldap.controls.php
LDAP controls examples: https://www.php.net/manual/en/ldap.examples-controls.php