getCacheEntry is not safe

Versioned update with a multi threaded Hot Rod client results in inconsistency. Some replaceWithVersion return true ignoring a version update executed in another thread. Here's a log excerpt of a concurrency stress test:

```
2014-06-20 16:16:56,798 INFO [PutFromNull] (pool-7-thread-10) count=462,prev=462,new=463
2014-06-20 16:16:56,820 INFO [PutFromNull] (pool-7-thread-9) count=463,prev=463,new=464
2014-06-20 16:16:56,831 INFO [PutFromNull] (pool-7-thread-2) count=464,prev=463,new=464
2014-06-20 16:16:56,845 INFO [PutFromNull] (pool-7-thread-9) count=465,prev=464,new=465
```
Here you see two threads applying the same replacement, from 463 to 464.

The issue appears a result of a race condition in Hot Rod server's protocol decoder. When replaceIfUmodified is received, the cache entry is retrieved to verify whether the version in the server and the version sent in the command match. However, the cache entry retrieved is mutable, and the value could change midway through this operation as a result of another thread updating the value. Please find below some log snippets showing this.