Upgrade to JGroups 4.0.13.Final

Interesting changes in JGroups 4.0.13.Final:

• Changed the way a coord leaves gracefully (JGRP-2277): instead of creating the last view itself, the leaving coord asks the next-in-line to create and install it. This has the advantage that the new coord can retransmit the view (if lost) as it's stil alive and simplifies code, because the path for graceful leave and crash is now the same.

• Reactive style of merging (JGRP-2281): when using MERGE3 and TCP, a merge could be only partial and multiple merge rounds would be needed, increasing the total time for a complete merge.
  This was changed by providing a new event which implements a reactive style of discovery by invoking a callback every time a discovery response is received.