s4/dsdb-schema: Index attributes on msDS-IntId value

s4/dsdb-schema: Index attributes on msDS-IntId value

O(n) search for dsdb_attribute by msDS-IntId value was
replaced by binary-search in ordered index.

I've choosen the approach of separate index on msDS-IntId values
as I think it is more clear what we are searching for.
And it should little bit faster as we can clearly determine
in which index to perform the search based on ATTID value -
ATTIDs based on prefixMap and ATTIDs based on msDS-IntId
are in separate ranges.

Other way to implement this index was to merge msDS-IntId values
in attributeID_id index.
This led me to a shorted but not so obvious implementation.