Provide capability to supply additional SASL properties

The createSaslServer method takes a Map of properties as an argument: -

http://download.oracle.com/javase/6/docs/api/javax/security/sasl/SaslServerFactory.html#createSaslServer(java.lang.String,%20java.lang.String,%20java.lang.String,%20java.util.Map,%20javax.security.auth.callback.CallbackHandler)

The map of properties is described as: -

The possibly null set of properties used to select the SASL mechanism and to configure the authentication exchange of the selected mechanism. See the Sasl class for a list of standard properties. Other, possibly mechanism-specific, properties can be included. Properties not relevant to the selected mechanism are ignored, including any map entries with non-String keys.

XNIO currently only supports the standard properties, however the mechanism-specific properties should also be possible.

I don't believe the mechanism specific properties should be added directly to XNIO as these could vary as you move to different providers, however the client of Remoting/XNIO should at least have an option to supply custom properties that will be added to the Map generated by SaslUtils.createPropertyMap().