(ITS#4987) imporvement to slapo-constraint

[manu@netbsd.org]

Full_Name: Emmanuel Dreyfus
Version: 4.4.4
OS: NetBSD
URL: ftp://ftp.openldap.org/incoming/manu-070529.ext
Submission from: (NULL) (213.41.141.172)


I modified slapo-constraint so that it can verify that an attribute value 
is bound to the existing values of another attribute. The purpose is to 
make referential integrity easier to obtain.

Attached is a draft patch for review.

Then there is the UI question. For now it's configured in slapd.conf like
this:
database        bdb
suffix          "dc=example,dc=net"
overlay         constraint
constraint_attribute title key netExampleTitle

Which means that add and modify on title will fail if the new value is
not an existing netExampleTitle value. I used the keyword "key" with
RDBMS referential integrity in mind, but I'm not sure it's that clear
in this context. Suggestions are welcome.

The update to man page is missing yet. I know.

Also, I had trouble understanding the style used in these sources. Is there
an official style guide for OpenLDAP?