Replace LDAP persistent search with syncrepl (RFC 4533).
    
    All direct operations with LDAP Persistent Search control are replaced
    by ldap_sync_* calls.
    
    Syncrepl code works in exactly same way as old psearch code:
    Only the DN of the modified object is re-used from the message,
    data from the object are fetched via separate LDAP search.
    
    Current code is not able to detect object renaming because we don't have
    UUID->DN mapping yet.
    
    Another limitation is that current code can't detect unchanged entries,
    so serial is incremented after each parsed LDAP object.
    
    Signed-off-by: Petr Spacek <pspacek@redhat.com>