New schema checks committed

["Kurt D. Zeilenga" <Kurt@OpenLDAP.org>]

slapd (HEAD) now populated the structuralObjectClass
attribute, validates the superclass chain of structural
object classes of an entry, validates that abstract
classes are superclasses of the structural object class
or one of auxiliary object classes of the entry.

In addition, the slapd now disallows changes to the
structural object class of an entry.

I also reworked the test suite to conform to schema.

Now that the structuralObjectClass is maintained, it
is now relatively straight forward to implement DIT
content and structural rules.

Enjoy!  Kurt