exposes register_certificate_map_function(), as better to return an error
if a plugin is compiled to use it and slapd is not built with HAVE_TLS
than failing with an unresolved symbol

alternate X.509 peer normalization function

Should reuse other DN routines.
Need to add various other DN matching rule functions.
This commit, combined with entryDN and slapcat -a, should
fully address ITS#3112.

RFC 3687. For now, both the attribute and assertion values are considered
as RDNs. Refer to ITS#3207 to find related discussion.

misc other cleanup

TODO:
	Fix transactional consistency
	Add client response control handling

rename dnPretty2 to dnPretty

	schema engine updated (but not schema routines so things don't run yet)
	nvalues mostly populated, enough for tests 0-2 to pass
	schema routines needs lots of work
	modify/mods codes needs lots of work

  to back-bdb, back-ldbm and back-sql (the latter with limitations);
- added handling of ":dn" attributes to extended rfc2254 filters
  and to matched value filter
- altered the behavior of get_mra() when a matching rule is given:
  now it checks whether it is compatible with the attribute syntax
  and, in case it is, the given mr is used.  In case of no type,
  the check is delayed when filtering