Updates, cleanups and improvements over the openldap23-* ports:
- Make sure that PKGNAMESUFFIX and COMMENT are correctly set when
building slave ports. 
- Remove RCORDER feature which is now deprecated.
- Move PORTREVISION related stuff to before bsd.port.pre.mk in
order to get the revisions actually work.
- Depend on CLIENT_ONLY and WITH_SASL to determine the package
- Make use of USE_OPENLDAP instead of rolling our own.
- Use WITH_RC_SUBR correctly rather than just specifying "yes"
- Depend on bsd.database.mk to determine the Berkeley DB name,
which makes it possible to use versions available from the
ports collection rather than making decision our own. 
- Disable threading as suggested by openldap developers if
BACK_SHELL is enabled. Indicate the fact when showing options.
- Update to 2.3.23
PR: 91902, 96752 
Submitted by: Gyorgy TEUBEL <tgyurci freemail hu> 
Sunpoet Po-Chuan Hsieh <sunpoet sunpoet net> 
Approved by: sem (mentor)
Other changes, blames and all bugs are mine.