merg #21 Remove hq refs - more refactoring
ACTIVEMQ6-44 - Internal error during UDP parsing

https://issues.apache.org/jira/browse/ACTIVEMQ6-44

The DiscoveryGroup should be resilient to failures on the communication.
We shouldn't kill the Loop if an exception happened during the read of the UDP messages.
Merge #22
ACTIVEMQ6-6 Add Service Extension Component

Adds a new service extensions components used to house any extension
points for integration and extension.  In addition this patch adds
initial extension points for XAResource wrapping.