Returns the RDN after escaping the characters requiring escaping. For example, for the rdn "cn=Acme, Inc", the escapeRDN method returns "cn=Acme\, Inc". escapeRDN escapes the AttributeValue by inserting '\' before the following chars: * ',' '+' '"' '\' 'LESSTHAN' 'GREATERTHAN' ';' '#' if it comes at the beginning of the string, and ' ' (space) if it comes at the beginning or the end of a string. Note that single-valued attributes can be used because of ambiguity. See RFC 2253