I made an update for the Hazelcast clustering plugin to Hazelcast version 3.1. This includes all the needed API changes to make it compatible.
It is not yet tested since currently I won't have a chance to test it in a clustered environment but maybe someone else could give it a try and tell me the problems if they arise?
The zip contains a diff file (I hope this is fine) and the two new Hazelcast JAR files. I also updated plugin version to 1.2.0
PS: Attached hazelcast.jar is the prebuild plugin to test in your installation.
Here's an updated version of the patch which just uses a newer build of Hazelcast 3.1 (3.1.2).