Fix: can't login when login or dn is in UTF-8

I wrote simple patch to fix issue, when some data (login or dn) is in UTF-8.
Without this patch you won't be able to login in this case.

For example I had situation when devise_ldap_authenticatable tried and failed with ```cn=graudējs,dc=example,dc=com``` or ```cn=graudeejs,ou=piemērs,dc=example,dc=com```

To avoid problems you need to force BINARY encoding for data that you send to ldap