[infinispan-runtime] Avoid creating Exception when tx is null

  * The contract for TransactionManager.getTransaction() states that it should
    return null when there is no transaction. The previous code was catching a
    NullPointerException to return null, which was far more expensive than
    just testing for null.
[core-api] BugFix: Use WeakReference to enable GC of deletageTx in JTADelegatingTransaction

  * TxMap holds a static
    Map<WeakReference<javax.transaction.Transaction>>,JTADelegatingTransaction>
    to enable collection of transactions used as keys.  However, because each
    entry's value (JTADelegatingTransaction) is strongly held in the map and,
    in turn, such value held a strong reference to
    javax.transaction.Transaction, the latter was never really collectable.
    This commit fixes this issue by turning the strong reference into a
    WeakReference.
Merge pull request #136 from smmf/fix/allow-gc-of-jta-delegate-tx

Fix/allow GC of jta delegate tx
[backend-infinispan] Fix typo in logger class
[backend-jvstm-infinispan] Fix typo in optional config parameter
[jvstm-infinispan] Close repository on shutdown()
Initial work on clustering support for all JVSTM-based backends

  * Use Hazelcast for group communication
  * Obtain serverId independent from the repository and use it to initialize
    DomainClassInfo
  * The first node to join the cluster is the only one responsible for full
    initialization of the Framework's infrastructures (e.g. DomainRoot, etc.)
  * Other cluster elements wait for the first member to complete startup
    before booting.
  * Update dependencies on Infinispan and JGroups so that they match
Move group communication down to jvstm-ispn only

  This commit complements cc88fe2, which first added support for group
  communication in all JVSTM-based backends.  It is considered best for now to
  keep this backend-specific, so, in this commit, we move such functionality
  to the only backend that currently extends jvstm-common: jvsmt-ispn.
Merge pull request #138 from smmf/fix/remove-group-communication-from-jvstm-common

Move group communication down to jvstm-ispn only
Fix typo in method name