CAPI-464: Alter user.memberof queries
CAPI-464: Alter user.memberof queries

This limits the potential contents of user.memberof to only the
'cn=operators' and 'cn=readers' groups.  If other groups are added, they
will not populated into a user's memberof field.  This is to overcome
indexing problems with the groups lookup.

joyent/node-ufds