Handling bad cn=config updates

[Hallvard B Furuseth <h.b.furuseth@usit.uio.no>]

If I modify olcDbDirectory of a BDB database to a broken directory, the
Modify returns success but BDB says "failed to reopen database" and
slapd shuts down.  Maybe other modifications can shut down slapd too, I
don't know.

It would be nice if slapd tried to restore the old config value, reopen
the old directory, and return unwillingToPerform or something to the
Modify.  However I don't know how hard that would be, or how obscure a
case it is.

For that matter, maybe if the Modify broke something it could return
some diagnosticMessage.  Not sure if it should return non-success since
that supposedly means the modify did not happen.  Though clients may not
display the diagnosticMessage if it comes with 'success'.

-- 
Hallvard