Treat unrecognized attributeType as bogus warning
Treat unrecognized attributeType as bogus warning

This can happen when searching and requesting attributes that are not recognized.

For example, the Net::LDAP Ruby library searches for `supportedCapabilities`
attribute when pulling back the Root DSE entry, producing this warning:

```
The attribute supportedCapabilities was not recognized as a valid attributeType.
```

As far as I can discern, unrecognized attribute types should be ignored by the
server. See:
https://tools.ietf.org/html/rfc4511#section-4.5.1.7
https://tools.ietf.org/html/rfc4511#section-4.5.1.8
NUBIC/ladle,NUBIC/ladle,NUBIC/ladle