Add SID related requests to the LDAP provider
    
    The patch adds support for BE_REQ_BY_SECID and BE_REQ_USER_AND_GROUP to
    the LDAP provider. Since the AD and the IPA provider use the same code
    they support those request now as well.
    
    Besides allowing that users and groups can be searched by the SID as
    well the new request allows to search users and groups in one run, i.e.
    if there is not user matching the search criteria groups are searched as
    well.