Implement DistinguishedName comparison with text

[adiroiban]

16.0.1 used to allow comparing a DistinguishedName with a text... but the implementation was broken as it relies on simple string comparison... and had no test coverage

The 16.0.1 implementation converting the DistinguishedName to a text and then compare it, instead of converting the text to a DistinguishedName and then do the comparison.

See the end of https://www.ldap.com/ldap-dns-and-rdns

Two DistinguishedName can still be compared. This is only about things like

dn.DistinguishedName('dc=example,dc=com') > 'dc = example, dc = dc`