As a part of the
http://issues.apache.org/jira/browse/DIREVE-210 issue I suggested to implemets RFC3673 support. The '+' attribute support was implemented in the 0.9.2 snapshot, but support of RFC3673 is incomplete because the feature is not published through 'supportedFeatures' attribute in the RootDSE entry.
Here is a quote from RFC3673 [section 2]:
Servers supporting this feature SHOULD publish the Object Identifier
1.3.6.1.4.1.4203.1.5.1 as a value of the 'supportedFeatures'
[RFC3674] attribute in the root DSE.