improper return of unavailableCriticalExtension (ITS#3308)

[kurt@OpenLDAP.org]

Full_Name: Kurt Zeilenga
Version: 2.2.15 / HEAD
OS: FreeBSD
URL: ftp://ftp.openldap.org/incoming/
Submission from: (NULL) (198.144.202.241)
Submitted by: kurt


In response to ITS#3283, I noted that slapd(8) is returning
unavailableCriticialExtension for recognized controls which
are approprite for the operation (when the control is
critical to an unservicable operation).  This behavior is
incorrect per RFC 2251 (as discussed in the LDAPBIS WG).
An appropriate service error (e.g., unwillingToPerform)
should be returned instead.