[IPA] SID allocation using DNA plugin

[Luke Howard]

Jumping in here without a lot of context.

One thing we did at Novell was to synthesise a lot of attributes, such  
as the password policy-related ones, from their native equivalents.  
This mapping was bi-directional: we built a small layer on top of the  
SLAPI computed attribute, search filter rewriter, and preop interfaces  
to drop in attribute translators.

-- Luke