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!
Does this flag need to be set for the return above where the cache loader returns non-null? line 452

I also probably don't understand cache writers enough either. A value being loaded by a loader isn't told to the writer?