Escape those RDN characters that are optionally escaped in the RFC(s)

[nwoolls]

LDAP RFCs for LDAP (2253, 4514, 4515) make escaping and # optional if they are not the first character in the RDN value. The current implementation of LdapDN.EscapeRDN() seems to follow these RFCs by not escaping or # unless it is the first character in the RDN.

However, some server implementations (e.g. org.apache.directory.shared.ldap) fall down on parsing these values. We can work around this but it would be nice to have LdapDN.EscapeRDN() escape the characters - maybe optionally? - that are currently only escaped if they are the leading character.

Understood it would be better to address the issue with parsing the values but this may not always be possible unless the author of the client is also in control of the server code.