Issue #147 - Add non-bulk Ehcache unit tests

Adds unit tests for the following Ehcache methods:

* get
* put
* containsKey
* remove(key)
* clear
* iterator
* putIfAbsent
* remove(key, value)
* replace(key, value)
* replace(key, oldValue, newValue)
This contradicts the test description. More generally I believe some of the tests are not necessary - once we have asserted that a `CacheLoader` sees no interactions when the `Store` holds the entry, there is no need to assert the same thing with different `CacheLoader` states. What do others think of that?