Support builtin Windows groups

This maps the gid (gidNumber) to an AD SID for builtin groups when
searching a group by gid (RID) between 544 and 552. In that case the SID
prefix is not the domain's prefix (S-1-5-21-dddddd-dddddd-dddddd) but
the BUILTIN SID prefix (1-5-32).

For example, if you add a user to the Administrators builtin group
(S-1-5-32-544), now you should be able to get this group through nslcd,
instead of receiving an error message.