Issue #143 Fixing Ehcache.putIfAbsent to return previous value

Now, I think all these Concurrent CRUD actually miss tests at the `Ehcache` level... Looks like this requires some new task!
It's actually meant this way, this is a `putIfAbsent`, so it only should return `null` if the value passed in was installed. So if it comes from the SoR, it should return the "existing" value, where the one loaded is supposed to be as if it always was in there.