"no structuralObjectClass" when lastmod is off (ITS#1904)

[simon@sxw.org.uk]

Full_Name: Simon Wilkinson
Version: 2.1.2 and CVS head
OS: Linux
URL: 
Submission from: (NULL) (213.122.111.254)


Current CVS Head (and 2.1.2) return Object class violation errors (with
"no structuralObjectClass operational attribute" as additional information)
when adds are performed against a backend with lastmod set to 'off'

This is because the slap_mods_opattrs function which picks the 
structuralObjectClass is only called if lastmod is on.

I've got some broader issues with the behaviour of mods_opattrs, which I'll
raise on the -devel list.