While ldaptls=1 provides an RFC 4513 conforming way to do LDAP
authentication with TLS encryption, there was an earlier de facto
standard way to do LDAP over SSL called LDAPS.  Even though it's not
enshrined in a standard, it's still widely used and sometimes required
by organizations' network policies.  There seems to be no reason not to
support it when available in the client library.  Therefore, add support
when using OpenLDAP 2.4+ or Windows.  It can be configured with
ldapscheme=ldaps or ldapurl=ldaps://...

Add tests for both ways of requesting LDAPS and a test for the
pre-existing ldaptls=1.  Modify the 001_auth.pl test for "diagnostic
messages", which was previously relying on the server rejecting
ldaptls=1.

Author: Thomas Munro
Reviewed-By: Peter Eisentraut
Discussion: https://postgr.es/m/CAEepm=1s+pA-LZUjQ-9GQz0Z4rX_eK=DFXAF1nBQ+ROPimuOYQ@mail.gmail.com