Memory leak in CacheStoreInterceptor

CacheStoreInterceptor leaks org.infinispan.transaction.xa.GlobalTransaction objects. Amount of live org.infinispan.transaction.xa.GlobalTransaction objects is climbing during cache work.

It is possible due to two reasons:
1. when cache is in async replication mode entries from both txStores and preparingTxs are never deleted (maybe like JBCACHE-1454 ?).

2. when cache is in sync mode (I tested on dist sync mode), entries from preparingTxs are not deleted in commit method (in case no exceptions raise).

So preparingTxs are never cleaned at all. Problem with txStores appears only with async mode.