(ITS#5721) Expansion on dncachesize behavior

[quanah@zimbra.com]

Full_Name: Quanah Gibson-Mount
Version: 24/HEAD
OS: NA
URL: ftp://ftp.openldap.org/incoming/
Submission from: (NULL) (75.111.29.239)


The behavior of the dncachesize setting when it is not ideal (2x) is not
documented.

Howard notes:

The DN cache is allowed to temporarily grow beyond the configured size.  It does
this if many entries are locked when it tries to do a purge, because that means
they're legitimately in use.  Also the dn cache never purges entries that have
cached children, so depending on the shape of the DIT, it could have lots over
the defined limit.

This would be useful to note in the slapd-bdb & slapd-hdb man pages.