Tree node move concurrency test broken

NodeMoveAPITest.testConcurrency() is broken, see attached log.

To summarise, when the concurrent moves begin, two threads are allowed to move, '/a/x' to '/d' and '/b'.

The result is that 'x' appears under both '/b' and 'd' in the end.

This test has been failing as early as https://infinispan.ci.cloudbees.com/job/Infinispan-5.1.x-JDK6-tcp/org.infinispan$infinispan-tree/142/testReport/junit/org.infinispan.api.tree/NodeMoveAPITest/testConcurrency/ but could have been failing from an earlier stage.